HD, I feel for you and the frustration. I think most people are generally giving the same big picture advice. There are just some smaller specific things that can be done different.
She's gone, there is no M now. What you are doing is moving forward with your life without making any drastic decisions or reacting with your emotions that could interfere with what could happen with you two in the future. Letting go and keeping out of her path of destruction (unless its involvimg you or the kids)so she can make her own life choices, and hopefully learn from her mistakes. Yes, fighting her on financials may not help but in some situations it's needed to protect yourself. Shea abused that situation so not much more you can do about it.
This is why we are polite and cordial, not because they deserve it but because we are being stronger and not reacting with our emotions.
Detachment would be a great thing to work on, go through the thread I'd you can, find a book to read on it. I was in that mental chaos not long ago and something clicked and now I feel like this huge weight has lifted off my shoulders, for the most part. Keep moving forward, things may not always get better but we keep getting stronger making it easier.
Accept what is, let go of what was, and have faith in what will be
