Leave your door locked and do not go out there. Move out of the house as soon as you can and tell your mom exactly why you are leaving.
I agree with Redyelruc. Can you leave out a window? If it gets worse I would suggest calling the police. Don't put yourself in any undue danger. Turn your lights out and pretend to be asleep.
next time Bunny, prepare some magic brownies and leave them in the Kitchen in plain view. drunk assholes will always take the brownie bate, and that baked THC will surely put him on his ass.
I hope that BraveSirRuben is only joking. That is the worst suggestion. He's drunk so he probably won't feel that much pain and he probably outweighs her by quite a bit. That is a good way to get her really hurt.
If you are really worried about your mother's safety, call the police. Don't wait for things to escalate.