I'm hoping a doctor who knows will answer this question.?

I have a granddaughter who is 19 years old and she seems to have a boyfriend who keeps asking her to get money. Just about every week he tells her she has to go get money and he doesn't care how she gets it. He abuses her mentally and physically. She cries everynight. She was living at his house for the past several months. She recently returned home, but she said she is still going to get the money he needs . She begs, borrows and steals for him and she says she loves him. The reason she moved out is to help the relationship get better she says, because it was pretty bad and she wanted to kill herself. I would take her to a doctor to get medicine, but the problem is that when she is with anyone else she is perfectly normal. She goes out with other guys and she is happy and normal. It's only with this guy that she acts like she needs mental help. I would hate to give her pills, when it's only him that makes her feel bad, but she won't leave him. What should I do?