Sandy,
You could play the game we used to with the kids...you know, trying to put a good spin on not-great news...
You can tell her, "Mom...I have some really great news! You will be home for Christmas! Isn't that wonderful?"
If she starts complaining, you can interrupt her and say, "Gee, I was excited. I didn't think you were ever going to go home from here."
Do you think she'd feel more positive after that?