What should i do about my bff?

my friend has been going out with this guy. she won't give me anything like his cell or his sn. and today she told me that he called her a b****. She's like help me help me what should i do. I said to break up with him cause it leads to worse things. but i don't think she'll listen, she never does. i mean i want to help her but she never ever listens. i don't know what to do.....