Taran's motive

I hate Taran's motive. I understand that she would be pissed at Sam for what he did. I just don't understand why it's all him.

Sam didn't force her mother. He didn't treat her well, but her mother had responsibility too. She chose to have an affair. She committed suicide and abandoned her daughter. AND she let her daughter discover her body.

Sam is a douche, but what kind of mother would do that?