Please Help! My friend is in an Abusive marriage

My best friend has been in an abusive marriage for 11 years. When she first started dating this man he seemed like the perfect partner. He was caring, hardworking, funny and seemed to care deeply for her. It was about a year in when I started to notice he wasn't as perfect as he seemed and slowly but surely he started to reveal his true colours. I will spare the horrible details but the abuse has gradually escalated over the years and although she swears to me it has never become physical I am still incredibly worried for her safety. He has a temper and is known to break things during fits of rage. They are in terrible debt and just recently it came to her attention he may be seeing someone else. They have been arguing constantly since with the emotional and mental abuse becoming more and more alarming and during a huge fight last week
he told her he was leaving. That night she stayed with her mum but Unfortunately the next day he decided he wasn't leaving and my friend has said she is "letting him stay" even though it is quite clear that he is the one calling the shots. She tells me she intends on working things out but after 11 years I don't know what to do. She is in serious danger and although she would agree with me she also refuses to leave this man.
She has seeked advice from domestic abuse hotlines, the police and her family as well as myself who have all given 100% support but she keeps finding excuses to stay or to "give him one last chance". How do I help my friend when she won't help herself? I've supported her decision to stay for 11 years but enough is enough. I refuse to sit back and watch her become another statistic.