@matana a squire isn't necessarily a knight in training, it's not like there is a training program for knights. they are an assistant/servant to a knight, often times too young to go to war. they may aspire to become a knight, but it isn't a given.
a sergeant is essentially a knight without the nobility. if they have land, it is basically subcontracted and they serve a specific purpose for the owners. they can be guards of the royal court, messengers, etc.
honestly i would call a knight who isn't a knight a soldier, whether they are a footsoldier, guardsman, pikeman, or likewise. they might still be adept with their weaponry but not noble.
a knight also does not have to be able to fight, it is a social status after all. if you are a knight, you own land or have done something to deserve the nobility. a sergeant would more than likely be doing the dirty work, and soldiers even more so.
of course this is all going to end up as fantasy anyway since, for the vast majority of the time, women were not in any of these roles. so it kind of doesn't matter what you call her, it's still likely to be historically inaccurate.