Help?

So my best friend has been with this guy for over two years now. at first they were cute and I supported everything, and now he's really abusive. he won't let her wear certain things, and she can't talk to certain people, he even got her pregnant after she said she wasn't ready, and didn't care when she miscarried. my other best friend and I have told her that he's abusive and she needs to leave him, and all she says is " I know". how can I help convince her to dump him???