I was unable to read above if there was an update to the situation.

I understand how infuriating and helpless the situation is.

Are you able to make a new tradition of your own? That would give you the opportunity to tell her Thanksgiving is off. An example is going out for dinner, get together on an alternate date, celebrating with non-traditional dishes she is not likely to like and hence be hesitant to attend.

When my mother was alive she would insinuate herself into any holiday. Making any kind of addition or alteration to what she felt was traditional would send her off into a you-are-wrong-how-dare-you-do-this. But, the end result was that she just wouldn't come and EVERYONE was a whole lot happier.