Don't feel guilty, obviously he fooled you both, that's how a man like that gets into a relationship, by being sweet in the first place, then once he has her changes completely. I know from personal experience.

He's abusing her with her words, and I'm sure she is hurt from all of this. It was brave of you to speak up to him, he needed to hear that.

There's nothing much you can do accept suggest and encourage your daughter by telling her she deserves to be treated better. It's up to her to decide what to do. Maybe if he received counseling or something he could change, but most likely he wouldn't be willing to.

So sorry this is happening, I hope your daughter finds strength through you.