I'd like to submit a contrary view to the other answers.

Daggers are bad and wrong
(for defence)

The main threat of a knife is thrusting, as it lacks sufficient force in strikes, or length in a slash, to do any real damage. Thrusts are very deadly, historically, but really terrible as a defensive technique. A thrust will kill the opponent, but it will often take several days for them to die, as the organ you have pierced festers. In the moment, however, it does not cause all that much pain. Compared to a hard blow to the arms, neck or head; a body thrust is not debilitating. (*)

Note that this is the exact opposite of movies, where any number of blows can be sustained, but a thrust is usually instantly fatal, leaving only enough time for a dramatic final line.

Since you are looking for a bodyguard, she does not care whether the opponent lives or dies, in fact alive but incapacitated is probably better. That way your would-be assassin can spend a while in the torturer's chambers, telling you everything you want to know. Knives, therefore are the opposite of what you want. They are deadly, but inneffective. You want:

A Quarterstaff

A 6-foot pole of hard wood (oak, ash, etc) held by one end and one quarter, strikes a blow which will easily break bones. It causes immense pain, but has a low chance of killing, thus giving you the best odds of disabling the assailant quickly. It also has a distinct advantage when it comes to disguise. Historically speaking, the staff was the weapon most often learned by women. As you say in your question, it is not considered seemly for a woman to wear a sword, but a walking stick? Even better, once you know the techniques of quarterstaff fighting, you can use this very effectively with a variety of household tools.

Garden hoe, laundry pole, rake, mop, etc are all very effective. The best, to my mind, is the broom. A birch besom is a staff with a thick bundle if stiff birch twigs on the end. As you sweep, the points are gradually filed into fine points. This forms a cloud of needle points, about the size off a face, which can be turned extremely quickly, since it is being held five feet back in two hands, and when thrust will gouge at the eyes and cheeks to great effect.

Since you say that your bodyguard spends her time disguised as a servant, she has ample reason to always have at least one staff weapon to hand at all times.

(*) For support for this fact we can look at two things, historical combat manuals and diatribes from the renaissance period, particularly around the introduction of the rapier, and also the modern epidemic of knife crime (particularly in the UK) where it has been shown repeatedly that carrying a knife actively increases the danger you face from knife carrying assailants, even if you kill them.

Is really offense the best defense?

As you stated in your question, your dual wielder is an emergency bodyguard, supposed to protect your princess in immediate emergency situations, with other bodyguards next door ready to intervene. So if this specialized female bodyguard have to act, it is for an action of seconds, maybe one minute if the male bodyguards are hesitating a bit to cross the door when the princess is screaming in her bathroom.

In my mind, what you want in this position, is to stall the fight before reinforcement arrive, and protect the princess. Daggers are a close combat, offensive weapons, with not much of a stopping power, and are designed to kill. if anything is thrown at your princess, what will you stop it with? if the terrorist/assassin just run for the kill without a care for his own integrity, will your dagger stop his course?

I wouldn't bet on it.

What seems to be better suited in this context?

This is only my opinion and interpretation of the situation, so It is just if you need it, but why wouldn't you use some classic feminine attributes?

an umbrella can be reinforced to stop some projectiles from getting to your princess if deployed quickly enough. it can be rather natural for some servant to carry an umbrella in case of rain, or to get some shade for the princess.

you can also hide a blade in this same umbrella. in the blink of an eye, you get a decent sparring weapon and a makeshift shield, without the inconvenience of going through you pockets to get your daggers.

But if an umbrella isn't part of your universe, why not carry fans? you can even have different set of fans to maintain the illusion that you are only a follower of the princess, giving her some fresh air if she ever need it, but one of them is hardwood reinforced to protect her from projectile, and another one is sharpened enough to severe an arm if one comes too close. Moreover, they can also hide a short dagger, so your dual dagger wielding female bodyguard is still an option, while offering some shielding to the one she is supposed to protect.

Dual Wielding takes a ton of coordination and training. But it's possible. Your biggest drawback in this scenario is that your lady Badass in waiting is supposed to be a body guard. She is not defending only herself but the princess. Two daggers is doable for one lady to defend herself, but a bodyguard has more to worry about. All you need to do is shift things a touch.

Since the bodyguard is in disguise as a lady in waiting, and given the time frame you have a ton of options. Her first priority is to get the princess to safety. This means she will be shielding the princess with her body, probably leaving her back exposed. I base this on watching the behavior of modern bodyguards and secret service men. they always cover as much of the person they are guarding as they can, and this is best done by facing the target, not the threat. They do this until either someone else deals with the threat or the target gets to safety.

In your case get at least some sort of thin armor concealed in the garments primarily on the back. Other areas that could conceal armor might be along the forearms and backs of the thigh. If your setting allows for those ridiculous ruffs and wimples, you could even stash a thin helm under the pointy hat and a steel collar under the goofy frills.
The armor will have to be fairly lightweight for concealment and to prevent clinks and clangs. Hopefully it will slow down the bulk of assassin weapons long enough, or if it doesn't stop the weapon, it should bind it up. The body guard will call for help, cover the princess and hustle her off to a panic room or hidden passage or whatever you have. That is the core strategy. Don't engage the assassin until the princess is safe. Once the latch on the panic room catches, it's game on.

Fans are possibly the most versatile. Keep a sharpened steel blade concealed in the slats. Even without the blade the fan can be used to defend. It's not built to stop the thrust of a blade, but more to redirect the point of aim. To deflect, rather than block. And unlike a dagger, a fan can be carried openly. Remember, most royals frown upon people carrying edged weapons too close. A dagger can be concealed, but it has to removed from concealment before use. A fan can be at the ready at all times.

A Parasol or umbrella could also be carried openly. It is a stick, it can hide blades, and when open can obscure the target from threats. Again, it won't really stop things, but can be used as defense by deflecting. It can also be used as a short spear. wrap the small blade in rice paper to obscure it at the end of the umbrella. Then just poke. Or hide a small rapier inside the umbrella as a whole. Or, yes, a dagger.

So get the princess to safety and turn on your assassin with the heavy dagger from the umbrella in one hand and the fan with concealed blade in the other. Her forearms will act as shields, her throat is guarded, and she can also seriously head butt with the helm inside the stupid pointy hat. For bonus points, give the princess herself a pair of slender daggers and teach her how to use them herself.

It's a good start

To quote Robert Heinlein

Specialization is for insects

Are daggers a good weapon? Honestly, they aren't a bad one, they've got all the advantages you've described, but make sure you're using the right daggers. If you're looking to stab gaps in armor, you want a stiletto. On the flip side, an assassin that's attacking the princess when she's taking a bath is sneaking around, so probably doesn't have heavy armor. You'd want a dagger with more substance, maybe something similar to a combat knife, or even something cleaver-like for psychological effect.

But take some more. The main disadvantage is range, obviously. A brace of throwing knives will offset that, good for mid-range fighting up to twenty feet at minimum and capable of killing people outright with good enough aim. A cloth belt is simple, but a braided one can be turned into a whip, possibly even tipped with a metal spike. Hair decoration can conceal lockpicks or darts. If the setting is right, they might have access to crude smoke bombs, which can be conceal in a canister. Poison is great too - a powerful paralytic turns a gash from a wound to the end of a fight, while keeping the assassin alive for interrogation.

As for armor - take a look of Gambeson, a heavy cloth armor. Medieval ladies wore quite a lot of bulky clothes, and while armor is noticeable, just cloth layers aren't.

Yes. However, I wouldn't go with them or only with them.

First, dual wielding is extremely hard. Having an off-hand weapon is different from dual-wielding. The later requires extreme coordination, skill and awareness or you may get in your own way. It doesn't give that much advantage unless you are borned to it (or trained from infancy).

Second, it is hard and unwise to try to parry with daggers, especially against stronger opponents. The force will still transmit and damage your hands. It is better to dodge. Your bodyguard will want to avoid any extended close combat. A single strike to neutralize or kill the enemy, otherwise she IS screwed. Or the princess is.

Third, limiting themselves to well understood and well known weapons are foolish. Their whole fighting style and strenght lay in their concealed nature. The best example I can think of are the Bene Gesserit from Dune.
What I mean: they had the Gom Jabbar, a concealed poison needle. They had special movement, body-language style to lower the enemy wariness against them. They used their Voice to their advantage, ...

Protecting is waaay harder than killing.

The bodyguard in question would not be a servant, but a lady in waiting. The duties of a lady in waiting can include helping the royalty get dressed and bathe and so on. It would therefore not be unusual for them to be in attendance at those times. (This is a rather prominent position. Think more executive assistant than maid.)

In medieval times, it was customary for everyone to carry a knife at all times. This is used for both eating, and general knife-based tasks. This is not a weapon. A lady in waiting carries things the princess might need. This could include her knife. This is also not a weapon. If those knives happen to be of an design that's useful for stabbing people, they're still not a weapon.

If both those knives happen to end up embedded in a would-be assassin, the design of the knives in question is the least interesting part of that event.

Hidden Weapons

The Japanese had the Tessen

Tessen were folding fans with outer spokes made of heavy plates of
iron which were designed to look like normal, harmless folding fans or
solid clubs shaped to look like a closed fan. Samurai could take these
to places where swords or other overt weapons were not allowed, and
some swordsmanship schools included training in the use of the tessen
as a weapon. The tessen was also used for fending off knives and
darts, as a throwing weapon

They also had hair pins which also doubled as a stiletto or throwing knives.

An umbrella can contain a cane sword and could also contain a hidden shield.

Armored Glove and a small riposte blade

The biggest downside of wielding two daggers is having no hand free to grapple, push, open doors, flip tables in the way of your attacker. The primary duties of your emergency bodyguard are threefold:

1. Recognize and stop the attack out of nowhere. - There is no time to draw any weapons or tools, if the assassin is good the bodyguard has mere moments to act and grab the princess or the assassin to make the attack miss.




2. Stall for time until other guards arrive or the princess escapes to safety. - It is not really necessary nor advisable to kill the assassin quickly. The bodyguard needs to prevent him from harming the princess and should also survive himself (since good bodyguards are hard to find) So grabbing, stalling, defending and incapacitating the assassin are good moves.




3. If the assassin attacks from afar or there are multiple assassins - help the princess escape to safety. This means opening doors, pushing bystanders aside closing doors behind them. For this to work the bodyguard needs at least one hand free and no big weapon, which could be a hindrance in tight spaces or while running.

If you want something traditional just go with a simple short defensive fencing weapon like a riposte blade. I would also add an armored glove/gauntlet (maybe leather with metal inlays) if the hand maiden can always hide one hand under her overcoat or sleeves - maybe pretending to be crippled on this hand or something like this. An armored Hand would combine the versatility of a free hand with the option to grab most blades by the edge, which would be ideal to stop an attack. The other hand could then wield a small blade for counter attacks, or a small riposte blade to defend against a skilled dual-wielder or fencer.

Daggers would be the weapon of choice for an assassin, an attacker. For a defender, not so much. To use it effectively means closing the range, when what you'd ideally want is to keep the opponent at as much of a distance as possible, delaying them until the protectee makes her escape or help arrives. Remember, the job of a bodyguard isn't to disable or kill the attacker, it's to protect their charge, and those can be two very different things. As mentioned, there are several weapons such as spears or staffs that would be better, but the problem is that they aren't very subtle and, magic aside, really can't be hidden.

However, your setup explains a way of overcoming this easily:

However, it is equally unbecoming for a male, guard or otherwise, to accompany a woman into certain 'female only' areas. (Bath, bedroom, etc.)

Given the situation, then, the only time the only bodyguards could not obviously armed (and men) would be in specific, non-public, locations. So there's your answer; you don't need to secretly equip the bodyguards; you equip the room. "Ceremonial" spears and shields on the walls. Staffs disguised as brooms or mops leaning in the corner. Things all over the freaking place so that the "maid" is never more than a meter or so away from something that is a hidden weapon, is a disguised weapon, or can be used as a weapon.

If the princess is travelling, this creates some problems, but that's easy enough to overcome, as propriety clearly indicates that her servants simply must check out bedrooms and toilets to see if they are fit for the princess, as well as of course she sleeps on her own linens because she's a princess and she has her own special blankets. So while the princess is outside in the public area surrounded by her very obvious guards, her maids are scurrying around preparing her bedroom, and unrolling all the weapons hidden in the blankets and sheets and setting them up.

No weapon.

A dagger limits you. An opponent with longer arms can outreach you or kick you. An opponent with a thick body can take the dagger thrust and keep coming. An opponent can foul the dagger in his robes. You drop your dagger in the toilet and your enemy flushes it before you can stop him.

And a dagger is obviously what it is. If someone finds a weapon like this on the bodyguard her cover is blown, permanently.

The only answer is kung-fu!. Your lady bodyguard is trained in the techniques: fighting a larger and heavier opponent, fighting opponents with various armaments, and so on. She has nothing but her brain and body and so nothing to blow her cover.

If serious stuff is going down, she is handy with the daggers as well. She just doesn't have any on her. The male bodyguard keeps extras on his person of the type she likes. Even if the princess is in the potty, he is right outside. He hands over the daggers when it gets bad and then he and the lady guard are back to back with the princess between.

Daggers seem like a bad choice for a defensive bodyguard. More the kind of weapon picked by the assasins.

But depending on your courts fashion, your maid may have quite fashionable armour options for protection. A renaissance or later dress may include a heavily boned corset which may be enhanced easily with some chainmail or plate parts. It is typical to have lots of padding and multiple layers of cloth all over, not that different to a gambeson, especially if tailored for protective effect. Such a dress tends to be actually quite heavy. Or take a look at the laminated linen armour called Linothorax, a bit like an ancient version of Kevlar armour.

For weapons you may want to look at spears, staffs, quarterstaffs, escrima sticks (usually dual wielded), combat fans, tonfas or similar.

Yes they would be a viable choice, unless the assassins are full armoured knights, but not a necessary one. Unless the lord is expecting fairly well armoured assailants then any weapon is probably surplus to requirements, good training in unarmed combat is more desirable.

No. As stated, the bodyguards' first priority is getting her charge to safety, thus any weaponry they have should be useful toward that objective. Daggers, as so many have mentioned, are offensive weapons, so even a duo of assailants would be too many for one bodyguard as one of the assailants could fairly likely reach the target. Instead, a bodyguard should be armed with weapons that hinder or slow down any potential threat so a retreat can be done as safely as possible. Caltrops, in medieval times where sources of light may be scarce, would be excellent options as any sneaky assassin-type would most likely have soft/silent footwear (or none at all) to be as quiet as possible.

Also, a throwing knife or dart may be useful. It has the benefit of range, and if used proficiently, can be enough of a deterrant to cause a would-be-assassin to flee.

It would also make sense to have something, which could be used as a makeshift weapon, in every room where regular bodyguards' presence is frowned upon. Like a broom, which may be used like a staff.

Thematically, the best defence against a dirty fighting assassin is another dirty fighting assassin, so concealed daggers would be a good option.

Who better to anticipate where attacks will come from than one trained in making those attacks. Who better to guide the Princess out of harms way than one who can out think their adversaries and leverage intimate knowledge of the castles secret ways.

Your bodyguard/lady in waiting shouldn't need to be carrying specific equipment to make her effective, she should be adept enough to make use of whatever happens to be around. Fire pokers, a bronze bust here, a mahogany chair there. Castles often have weapons hung on the walls or in the hands of statues and the assassin should be able to adapt to any of them as required.

Better still, make the Princess her own saviour. The assassin isn't just her lady in waiting and bodyguard, but her fencing coach and mentor too.