I say follow your dr's advice and limit contact. I've gone for periods of no contact for as much as a year with my AM and much longer with my AF. Now, I am in limited contact with AM.
You don't have to put yourself through the anxiety of Christmas, or any other time. You don't have to focus on your sister's mess, or what your mom is saying about it. You have your own life and you can make your own traditions. You can create a family around you that involves your friends. You can find the people you want to spend time with, and spend time with them. You aren't required to spend time with family or talk to them just because they are blood relatives.
I understand the moving away thing. I have tried it before, too. I haven't gone to anotehr country, but I have gone across to other states. One of my friends put it very well. He said that no matter where you move, you still have to deal with yourself. He had moved from the west coast to the east coast!
He was right. I moved about 4 years ago. There are advantages of the new place, but I still have to deal with myself. Moving isn't a magic cure. My RABF thought that moving would help him with his drug addiction, and relapsed after about 9 months. He's in recovery now, but it took him a while to realize he couldn't just run away from the addiction. In my new town, I have a psychiatrist to help me. I certainly wasn't able to run away with my problems with depression and anxiety.