Yeah, the whole psycho slave thing definitely feels like a way to make sure nobody hurts her again. Sort of a coping mechanism that developed into a kink. Like they say, children engage in play to cope, adults engage in "play" (kinks) to cope.
Plus, I don't think she did anything worse than the average monster girl you encounter? Like, she even offered you the possibility to back out of the hypno thing at any time.
She feels less like an evil master mind and more like a person with severe trauma.
Her background makes it kinda rough (and it's way darker than anything else in the game) but it seems violence like that was just way more frequent? I mean, Feng and her just got attacked by a group of adventurers that killed Feng with no second thought so...yeah. But probably best not to get into that part too much. Don't wanna start a discussion about monster girl war morality.