This is not your mother. This is her cult indoctrination. She is a victim of undue influence. While her authentic identity would more than likely help in whatever way she could, the cult identity is in the driver's seat.
I believe if you can understand it's not her that is the problem, it's the cult, while not solving the problem, it help cope with it. The good thing is you are in communication with her...many of us who got fully committed to the cult at a young age no longer are in regular communication with our parents, relatives, and friends who are still in.