I agree with Aegis. Just cut your family visit short. She's got her own history with Christmas. Maybe she's not ready to share it with you. You don't know. I understand your concern and your instinct to take care of her, but you can't always do that.

Definitely call her that day, let her know you're thinking about her.

I've spent Christmas by myself before. It really wasn't that big a deal, but then, I'ts never been my favorite holiday. Maybe she feels the same.