She should've just stayed with her dad and never confronted her mom about her... conception.
From what little we saw of him, though he seemed to have similar issues to her mother (except trade anime for goth) he appeared more stable and less extreme. Plus, we know he actually has a job. I somehow doubt her mother does given her personality and issues. I assume they probably live off his alimony and child support payments, which means he's probably doing alright. He probably owns the book store he works at, or at least is a manger there.
Though, I suppose it wouldn't have mattered if she decided to stay with her dad, as it's heavily implied that he's afraid of her mother, and you know she would've come for her at some point anyway.
There was no escape. It would've only been delaying the inevitable.