Perhaps we could have one "female peasant" troop/troop line per kingdom, based off female figures of their respective cultures. For the Swadians, we could go with a lancer cavalry, Joan-of-Arc styled line; maybe the pre-existing Swadian Lancer could be changed for that, with the regular male veteran recruits becoming the heavy cavalry Praven Knights, Dhirim Captains, and Men-at-arms.
The Nords obviously have their Valkyrie troops, leaving the matter of them being either foot-based or one of the few cav units Nords have to the developer, who'd be better at balancing it.
The Rhodoks could have a "Home Guard" unit; given their mountainous terrain makes me think of settler families, and the hardy women of such families who were just as used to swinging an axe or hunting game as keeping the house clean and cooking. So these would be light skirmishers using the hunting/light crossbows and 2h-axes, complementing the heavier regular infantry of their armies, maybe a foot-based version of the unique mounted-crossbowmen on the border of the Rhodok and Sarranid empire.
The Vaegirs could probably end up with something similar to the Rhodoks; a light skirmisher unit, but with a focus on archery over crossbows perhaps. I think there are plenty of people here in this sub-forum that could come up with a better idea then this, though. The entire Vaegir infantry is based around light, hard-hitting infantry anyways, so maybe we could go in the opposite direction and give them an angle of hardy, turtling troops. In essence, the Rhodok women would be Vaegir-ish, and the Vaegir women would be Rhodok-ish, if that makes any sense.
The Khergits already suffer from a lack of diversity, more so then Nords and Rhodoks who have a wider access to different types of troops; crossbowmen, archers, light cavalry, throwing weapon troops, 2-handers, etc. What if we have a hypothetical situation, the Mongolian equivalent of Japanese onnabushi? So Mongolian warrior women who tend to the horses of their husbands to keep them ready for war, and then on the battlefield follow in the steps of their husbands on foot, using either archery or polearms (possibly both?) to act as support infantry and give the Khergits more of a fighting chance in sieges as opposed to their single dedicated infantry unit, the low leveled, poorly armored spearman.
The Sarranids... my immediate thought is of those belly dancers, but armed with swords. Except I'm trying to be as grounded as possible, and women running into battle wearing nothing but silk veils and expecting to put up a good fight against their primary opponents, men armored in chainmail with pikes and crossbows or men riding horses and firing arrows and bearing lances is a really dumb idea. Definitely need more thought on this.
Of course, we could always just have one neutral Sword Sister line; that worked out fine in the base game, and there's no reason it wouldn't work out fine here.