How to tell MIL she's not invited...

MzCurnett8886

I posted in my BMB but still need advice on my best course of action since MIL is a huge drama queen:

MIL stated that she would throw her own shower because she didn't want to be in the same room as step MIL. Okay, that's fine, we worked out that the guest list was her side of the family and family friends. We figured out a date and all was well.

MIL Facebook messages me that she has changed her mind and can be in the same room as step MIL and that she no longer wants to host a shower, here is her list of 25 guests that she has let know that SIL (step mother's daughter not her own daughter) is the new hostess. SIL worked out her budget with me which was DH's dad's side and about 50 people.

My sisters are also throwing a shower for my family/friends/family friends. My sisters detest MIL for her behavior towards them and at both my bridal shower and wedding. They refuse to allow even just her and DH's sisters because of past offenses. She agreed to cohost, invited all her relatives (35people and told them kids were okay when they weren't) then didn't contribute food, beverages, d?cor, came late and then didn't offer to set up or clean up. She said that either of my hosts 'could' include these people if they really 'wanted' to.

My sisters both don't want to take her extra guests on, nor I think should they. They figure she has to be the one to pay for her tacky behavior. How do I tell MIL that she and her guests don't have an event to attend? She's trying to hand them off on someone else's bill.

ETA: DH can not get involved since he's deployed and trying to switch from his current job to bomb squad. He has much more important things on his mind than my baby showers.