Have you sat down with your sister and said, look here, let's see can we come to an agreement? I know, easier said than done, but it might be worth a try. Failing that, just ignore her and see if she goes away. By that I mean, don't let her get under your skin. I can't remember it exactly, but there's a verse in the Bible that says something to the effect of, when you are kind to someone who is unkind to you, you have heaped hot coals upon his head. ;-)

Mack, I have a friend who doesn't send Christmas cards or give Christmas gifts. He does those sorts of things all year, rather than just at the holidays... so I guess he really does keep Christmas all year-round. :-)