I'm sorry, I don't have any answers for you nor any suggestions that haven't already been said. I do, however, send you my deepest sympathy. I do know what it is like to try & deal with a person who is determined to have it their way. Perhaps try a bit of reverse psychology on her. Start smothering her with attention, not a minutes peace. Stay in her face consistently and always agree with everything she says. Some people do these kind of things for attention. That's really all I have.
Its called murder. KIDDING! I swear! No, first thing is sit down and have a talk with the bf. Then once everybody is calm you and him have a sit down with the mother and explain the problem and your feelings clearly. Try to find a solution that works for all parties involved. However, at the end of the day duct tape and a chair works too. Kidding again!
It's HIS responsibility to make her stop. Not yours. You will be the villianeven more than you are now if you try.
Sounds like she has a co-dependency disorder. Maybe google it to double check if it matches up.
Just remember, if you marry him,, you're stuck with HER too, the rest of your life.
give her some muffins
sit with your bf,look deep in his eyes and tell him this.He has to grow up.
then he would have to call me .