How To Help A Friend Deal With Depression

The best and only thing you can do for your friend is to get her to a competent, trained counselor.

1) Is the boyfriend so violent that she's afraid to dump him out of fear of what he might do?  If so, the police would also need to be involved and you'll need to push her to use that option.

2) Is she afraid of being alone if she dumps the boyfriend?  Then do her a favor and be there for her after the deed is done.

However, please note that depression is a medical condition.  The stress in her life is only a contributory factor.  For an introduction to depression from a reputable source, visit:
-  www.nimh.nih.gov/publicat/depression.cfm