Lost, we have very similar MIL problems. I have been trying to take your lead, and not allow MIL to get under my skin. She hasn't talked to me in 6 months, yet I know she is lurking, trying to cement this D pattern and move W on to other things. I'm going to let that go, and be supportive to W's attempts to be independent and responsible for her D choices.
A rough point coming up is W being held to the custody arrangements that she requested. Currently, she's moving toward asking me to watch S5 over the summer in a 50-50 arrangement. I love S5 immensely, yet have incredible work obligations I committed to so as to pay off the debt I accepted as part of our D settlement. Further, I need the time to win my tenure here at school, and finally, the biggest 'sin' I committed against W according to her last Fall was not providing well enough for her to stay with him more.
Now is her chance to do so, and she seems to be wanting to fill that time with more career stuff. I think I will let her sit with this reality of her D agreement, and use the time to better set the table for S5 and I in case she decides to give him to me completely or for the majority of time. My biggest hope would be that she sees more quickly that D sucks and that our M was a far better option.
Sam, thank you! As you can tell, I haven't given up. I'm disappointed the D went thru, and yet I know that W has some definite individuation work - becoming her own person and gaining a true identity - to accomplish. On my part, surviving these next 6 wks of intense teaching, then enjoying a trip to see my folks with S5, all the while trying to keep my changes in place.