I talked this same friend through an abusive relationship & breakup.
It sucked to watch her hurting once I realized her boyfriend was a real jerk, but it seemed to me that the best thing to do was to just keep asking her to tell me how she felt & what she wanted. She didn't need to be TOLD. She needed to speak for herself.
I certainly couldn't make her believe she deserved better, but I could encourage her to come to that conclusion from within.
She didn't need me. She needed HER.