SHe is your spouse’s Mother,,you treat her as you would treat your own and don’t discuss politics with her.
I wish it were that easy. Each time before we visit them, we have an agreement to refrain from any political discussion. Each time, you guessed it, they break that agreement. Usually it begins with “I know we aren’t supposed to talk about politics, but...”, which is then followed by whatever bomb they feel like throwing over the fence that day. I have kept quiet for eight years. Only once have they kept their word, this last Christmas.
I think the only way I am going to be able to keep my sanity is to stay away from them, and fight the socialist politicians on the local, state, and federal level.