What is her point, if she is not interested in the M? It will, however, keep your wound open and you will probably be upset at whatever she has to say during the session.
Just brace yourself for anything and have zero expectations of it helping "you" at all. She isn't going to help the MR or to help you in any way. She is going for whatever "she" can get.

Yes, the WAS are unbelievably selfish, and I think you have only just began to see what will probably get worse before it's over.. Have you thought of setting up a schedule for when the kids stay at her place? You need some time for yourself, and she should act like a parent and keep them.

It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!