I handed her a note that I had written explaining that she had crossed a boundary that I clearly verbalized and that I needed her to move out of our home.
You still don't understand boundaries. You can't force her to leave the home. So, that kind of backfired, IMO.
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So, it’s 4 days till Christmas, do I move out or wait till after the holiday? I want some space, but I have two kids that are young enough to still bank on Christmas as a special time of year. My youngest still believes in Santa... I don’t know what to do... any advice?
You should have thought this out before you decided to tell her stuff you won't or can't back up.
Don't leave the house four days before Christmas. Focus on your children. Stop interacting with her. She does not care about your feelings, so STFU. After Christmas, you need to decide what you will do.
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!