Does controlling behavior lead to violence?

My friend is in a relationship where her boyfriend controlls everything, by everything I mean even her paycheck. When she goes over his head with her money, he seems to get very agiated. Sometimes he says cruel things to her, and I was wondering do you think it would escalate into physical abuse? I'm starting to see some mental abuse, and I have tried to talk to her but she refuses to listen. She thinks that he has only her best interest at heart. I on the othe hand think he has only her money at heart. What should I do? How can I help her see the light before (if) it turns into physical violence?