Maybe you can get your whole family in on a "let's make her as uncomfortable as possible on Christmas" game... Everyone bring a box of saltines, a can of black olives. a stalk of celery, un-cut, not prepared in any way. A bag of raw cranberries... a can of pumpkin pie filling. Set it all out on the table, cross your arms. Everyone stare at HER and glare. Roll your eyes, ignore her and converse between yourselves if she starts up. If she gets loud, turn your backs and settle into small, private groups. open a can of olives and DO NOT offer her one. Eat the whole can. open a few small gifts, of which NONE has her name on it... and say goodbye, shove everyone out the door. It'll be all over in about twenty mintues and will hardly cost you a dime.
I think maybe she'd get the drift.