I might be a little young to meddle in this. But I've seen a lot, so maybe this helps.

My niece was in this abusive relation with a guy in france. He was just a horrible person and everyone could see it, except her. My aunt kindof tried everything possible to make her stop seeing that guy. NOTHING helped. Untill my grandmother told her to turn things around and all of a sudden be VERY interested in the relationship. Be approving! Invite him over all the time. This was a very big step for my aunt because she feared it would make things worse and get her to grow even closer to this guy. But what happened was, that my niece got very confused about this. She ended up dumping him because there was no "resistance" from her parents anymore.

So if you have tried everything possible and nothing helps, you might just consider taking it from a different angle. Resistance makes relationships exciting. It is probably because of the danger, she is attracted to his guy. This is very hard to understand, because there is nothing logical about this. But in some situations, when there is no resistance left, you can start seeing flaws.

Remember that I'm not saying this WILL help, because it is not always the solution.
I do hope you find the right one!

Love, Demi