She has told you he couldn't be stopped. She was a victim as well. I am sorry all of you have gone through that but you can't look to you mom for validation. It just won't happen.
She may be codependent but she says she is happy and things are fine now. For her that is probably true. Chances are she won't change. She is who she is. You have no choice but to accept it. Doesn't mean you have to have a relationship with her. We can't expect others to validate us or to see things our way. You have to find it inside yourself.