She probably refused to sign anything b/c of some legal hold. Don't know if that would hold up in court or not....if she had signed it. But since she got part of her things and you think she may come back when you are gone from the house, couldn't you change the locks? If you have given her a certain time frame to collect her things and if you think she may get more than agreed upon.
Just a thought.
After this invite to go to the C's, I would not bring it up anymore. You have more than made your feelings about the M known to her. I think if you persist, it is pursuing.
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!