I'd say that in this Medieval setting, women would better fit in the army as Lieutenants. Meaning thta they would very rarely fight, but give out orders and influence morale.
Did not read about any woman commander during the Battle of Brenna though.
As far as spies, assassins and infiltrators are concerned, women have an important role in Nilfgaard's forces I would say.
I can't see how well they would do as "footmen". Most Nilfgaardian Units use heavy armor, and while women are able to wear it, their body mass is significantly lower than that of men. So technically it would be a waste of resources, since body mass would play a very important role in a close quarters, heavy armored fight.
I'm sure women would make fine archers though.
And then again, they could also be medics. Or accountants. Or even engineers.