This novel I'm working on is driving me up a wall. Or into one, maybe. My protagonist is a teenage girl who's adopted by a very young foster mother. The main conflict is between my MC and her foster mother's father, a charming, manipulative psychologist. I'm having a problem finding a reason for him to despise my MC so much that he'd spend years tormenting her by sabotaging relationships, having her stalked, etc. He does the same thing to his daughter, but to a lesser extent. (Since she's an adult and a bit tougher, there's less he can do to her.) The story's urban fantasy, so there's lots of room to play, but I can't figure this one out. Ideas, anyone?