members of people in abusive relationships?

My sister has been in an abusive marriage for a decade, and it has been extremely hard not only on her but the whole family. In August she finally filed for a divorce (complete with restraining order) but called me last night to let me know that she’s giving him another chance. I want to be as supportive as possible, I don’t want to allow him to further isolate her, but it is really really hard to watch someone you love so much go through all this, and go BACK to it after getting away.

Thanks.