I'm not impressed with Lita here, for two additional reasons:
1) The Chinese food was her suggestion. Look, I often eat Chinese food on Christmas, but I would never suggest it as a Christmas dinner for someone who was actually celebrating Christmas. Particularly if that family had a tradition of eating traditional "Christmas food" (turkey, goose, whatever). Saying, "oh, let's just order Chinese" is denigrating the importance of the event.
2) Lita and the OP's dad are enough of a social unit that he spent Christmas eve with her family, instead of his own children...but the next day, Lita can't possibly leave her children to spend time with the OP's family. Seems like she's prioritizing "her" people over "his" people. I wonder how the OP's dad feels about that.