So yours is a vanisher, mine a clinging boomerang. However mine too reverted into acting not just as MIL which really upset her as she despised how MIL treated others... Apple/tree right?
I did mediation twice, yes ... Twice. Neither time went through even though the second time I was at peace with it. I have some advice, well... Maybe not advice but this is what I did. I went in dressed as I would for a business meeting, I also adopted that mindset, I knew my rights, what I was not willing to settle for and I was not going to give w one penny more than what the state would recommend, not out of spite nor pride but if I gave a dollar more than I would have needed to it was going in her pocket and in my mind I was stealing from my S. She wanted it, she would need to feel all of its consequences I got a haircut, and went in happy and at peace. To that point I did all I could and made so many changes I looked at this as a final chapter to a book... Was a good book but I knew there was a better book ahead of me to read, I even shared a joke/story with w in the meeting room as she attempted small talk, I can't tell you how much this confused her. Your w is in crisis, no other explanation for her actions, actions which have serious life altering consequences.... Ones she is not currently equipped to handle, I seen this as a way to love, if my w needed the divorce to finish her journey, I was more than willing to set her free. She very well may need this to hit bottom, keep in mind she is suffering and in her mind she is scrambling to find anything to get rid of the pain .... She must exhaust all options before she actually can do the work Sorry you have to do this, been there and it's painful, I pray you find a bit of peace in all this knowing it's her journey and she feels this is the only path, tough love proves she has to figure it out on her own