The title of this piece is misleading. You have not been cut off, and you actually end the piece threatening to cut her off.
One thing that is interesting and can be a life lesson (should you choose to accept) is you refer to the incident happening when you “came home” for Christmas. But, that’s her home. Presumably it is not your home since you specify that you speak to her by phone, sometimes with long breaks in between. This all suggests you live somewhere else. The point, then, is that if you troll people about politics in their own home, you will get a predictably bad response and put relationships in jeopardy. Maybe that “At least he’s not Hillary” zinger was worth it to you. If so, that’s your prerogative, but you are complicit in the tension that followed.