It sounds like your mom is severely depressed and is relying on Fox News to give her dopamine blasts to cheer her up.
Even so, you have to let her go. Wearing your heart out trying to get your family together for Christmas will do nobody any good, especially not yourself. Keep a thread of connection by sending her cards that say things like, "It would be nice to meet" or "How are you?" with your latest address and email and phone number at the bottom.
Keep the bridges open. Yes, it's possible she'll go to her grave a Trump believer. But it's also possible that one day you'll get a phone call that starts with an embarrassed cough.