Is it possible to only see her at her own house?
Don't invite her to family functions.
My step-mother was like this. If you gave her the moon it was not the stars. I took my dad aside after a few years of this, and told him that until she changed she was NOT allowed in my house, PERIOD! He was welcome any time, but if he showed up with her I would not answer the door. Life went on without them.
It took two years, but finally she was at least able to show up, be quiet, and fill her book of memories with all the sh------- food we served, our poor taste in furniture, how we went out of our way to make her feel slighted, terrible child rearing techniques.... ad freaking nauseum. But she did it with her mouth shut and pretended to have a good time.
She died lonely and alone several years ago. You reap what you sew.