She drove 450 miles, was ganged up on, and treated deplorably. She was the entertainment for the ‘family’. If you want more of a behavior, you reward it. You cannot change people - you can only change how you interact with them.
I have no use for ‘families’ like that; I’d rather be an ‘orphan’ and happy. Who would want to sit down, in a hostile environment and “Pretend” they are enjoying themselves? I can think of infinite other places to be, and other things to do - that my spouse and I would actually enjoy.
Take Mom out for dinner somewhere nice, before or after the Dinner with the boor. Why put up with him?
Family is family. I’d give them another chance: “Oh, I don’t want to talk about that - the argument last year made the visit unhappy for me. You’re my brother; I love you; let’s stay away from our differences.” You never deviate from that message, because giving them the answer to the political question is the reward that reinforces the behavior. The visit is a visit.
And put up in a hotel. Walk out and eat nursing home turkey with mom if you have to.
I’m hosting Thanksgiving and politics is banned this year.
No matter the circumstances, it’s pretty stupid to put yourself in that situation.