Well, it turns out the father is into incest. My gf is no longer my gf and, now that we're married, she confided in me that he hates her because she 'left' him. Clearly a very sick man.... But not as sick as the mother who is, to this day, jealous of her own daughter for getting more 'sex' than her from her husband.
And in case anyone is interested, he got off without any charges and I suspect my mother in law of helping him out with that despite being in the middle of a divorce at the time. It wouldn't be the first time that she helped keep him out of prison for assaulting their own daughter. What a disgusting family. I'm glad we moved away.