I like to create imaginary characters and events around a real historical situation. I want readers to feel: OK, this probably didn't happen, but it might have.
When I'm writing a woman character, I don't think, 'What would a woman do?' I just think, 'What would this character do in this situation?
I don't think there's any great mystery to writing female characters, so long as you talk to them. If you lived in a monastery and never met any women, maybe it would be difficult.
Thrillers have been traditionally very masculine books; the women characters often rather decorative.