Have this last Christmas day with your Mum and next year spread that Christmas day out.
As children we saw my maternal Grandmother (lovely) on Christmas Eve, Christmas day was just us, my parents and my sisters, boxing day we saw my paternal Grandmother (nasty old hag) and we did it in that order so that she couldn't ruin Christmas for us 
I am lucky to have a good relationship with my in-laws so this is how Christmas pans out for me, Christmas Eve is just me, Dh and our children, it is sacred and no-one visits.
Christmas Day - up and presents opened.
Dive in car and 1 hour drive to my sister's house where all my family go for Christmas dinner, present opening afterwards (My older sister works in a theatre so only has 2 days off at Christmas)
Back in car for short 20 minute drive to in-laws, present opening then buffet meal with sil, her partner and parents in law.
Boxing day - chill and relax, 27th back to that theatre where my sister works for their Christmas production and back to hers for food and drinks.
Chill day, then 29th in-laws here at ours for food and chat that we never get chance to do on Christmas Day.
It is hectic, but I love it and it has been this way for 17 years.
Set your own version of Christmas up now. Stand firm, ignore comments from her, I tend to have a mantra in my head with people who are arseholes (sometimes it is from Peppa Pig, when Madam Gazelle says "you are beautiful swan, with grace and beauty") usually when someone was commenting on how huge my pregnant belly was and questioning whether it was twins 