Mother in law advice, please help?

Sounds like implementing the advice everyone has given you so far hasn't helped her at all. Leave a letter inviting her back into your lives with your FIL and tell him to choose his wife. Make sure he has your contact information and knows that either of them is welcome back in your lives at anytime but right now you have to do what's good for your family and he has to do what's good for his. Hopefully your MIL will get out of her self-indulgent tantrum soon.