I have this friend who is....

In a mentally abusive relationship. He has completely controlled all aspect of her life and is destroying her confidence. They have been dating 6-7 months and she claims that she is in love with him. I am constantly reminding her, pointing out things about him that are red flags but she doesn't listen. I don't know how to convince her, I'm worried that eventually this relationship will turn abusive... What should I do?