In the setting of a royal court in a stereotypical 'medieval' low-fantasy world, the royal princess must obviously be guarded. Assuming this society sees it as 'unbecoming' for a woman to be armed, any offical guard assigned to her would be male. However, it is equally unbecoming for a male, guard or otherwise, to accompany a woman into certain 'female only' areas. (Bath, bedroom, etc.) Unfortunately, those sneaky assassins have no concept of honor or common decency and will happily barge into these areas to perform their distasteful task.
Enter the covert bodyguard. She is a woman trained in typical servant skills, but she additionally receives rigorous combat training. She is expectd to stay hidden, seeming to the world nothing but an unassuming domestic servant, perhaps a little more 'attached to the hip' to the lady she serves than most servants. Only when her charge is threatened does she spring into action. This means her weapon of choice must be easily concealable, she will not be wearing more than the lightest of (concealed) armor, and she must make up in visciousness the advantage that an assailant has in preparation.
In combat, this bodyguard's first priority is to get her charge to safety. She will prefer running away over engaging, and only when there is an enemy between her and the nearest exit will she draw her weapons. When she does draw steel however, it means that there is an obstacle that must be removed, and this obstacle must be removed as quickly and effectively as possibly to minimize the time they have to bring their greater physical strenght and better weaponry to bear.
In this situation, the advantages I see for dual daggers are the following:
- They can be (more) easily hidden
- They are relatively easy to wield
- They can be used to target weak spots in heavy armor
- There is a certain psychological effect to being charged by a screaming woman, slashing at you with knives in both hands
- Using both hands allows more flexibility in attacking, especially if the wielder also happens to be ambidextrous.
There are of course also disadvantages:
- They are only light weapons, less effective against heavy armor. This is mitigated by the average assassin being a sneaky killer in light, perhaps medium armor, rather than a soldier in full plate.
- They do not allow for using a shield. However, a shield is not easy to conceal and as such not an available option anyway.
- They require extra training to use compared to a single dagger. This is perhaps the greatest disadvantage, but I imagine the psychological factor in combination with being able to use either hand to strike gives much greater flexibility in those precious initial seconds she has against a surprised opponent.
Would this be a valid weapon choice for a concealed bodyguard?
TLDR: For a bodyguard that is expected to remain hidden unless necessary, with the express purpose of getting out of a sticky situation as fast as possible rather than standing and fighting, would dual daggers be a viable choice?