I dearly love stbxMIL, but don't particularly feel like being very supportive of W. I don't know if it's better to remain NC, or respond with something like "Wow. That is terribly upsetting. Thanks for the update," or something a bit more supportive of stbxMIL.
Given this previous comment you made:
"I've already told her via email that I can't be her friend anymore."
I would stick to something brief like your first comment.
