Sasha not being a virgin there is a bug. She definitely is.
As for her masturbation stats, that's a bit of an intentional joke. From a Discord conversation between me and Atemsiel:
A: I do find it kinda funny that all the girls in the game are apparently a bit shit at masturbating
T: Nah, it's much more likely for most women to fail to masturbate to completion.
A: Except Sasha, who I think has basically a 1:1 KD
T: Heh, yeah, she does. I found that hilarious.
A: Sasha don't play
A: or rather, she does
A: and she's fucking good at it
T: She sticks with it. She starts something, and it gets finished.