From what I understand, their genitals/pubian region have been seriously altered in the process of implanting youki flesh, making the view horrible enough for mercenaries to lose their will to rape.
They have been enrolled as young pre-teen girls, so the modifications clearly altered the development of what should have been their natural woman body.
Then, their training and upbringing probably doesn't let much room for proper woman feelings/mindset/emotion set.
Both in their body and development from preteen, to teen, to young adults, there's no room for womanhood.
So I agree in thinking it's hard to rely too much on their gender to make asumptions.