Don’t tell her what to do; talk to her and listen. Offer your help, but understand that to leave or not to leave is her decision. Respect it. And tell her you respect her.
Acknowledge the pain and turmoil she is in, most especially the emotional turmoil. If she doesn’t leave him, don’t give up on her leaving him. Give her love, respect, support, and time. It’s going to take all of that.