traditin culture or religion are no excuse for anything
by the way if you have a girlfriend u have no game -tom leykis

Have you seen Tom Leykis? If it wasn't for his money, he wouldn't be able to even beg for pussy...he sets up this tough guy image, because he is a insecure douche
Straight Talk, No Chaser...you can either politely show the error of her reasoning, or mention it to folks---causally, and they will agree, prior to x-mas, therefore influencing her decision...or have it at her house, and like someone said, mention it, casually during dinner, within earshot about it...yet praise her on the wonderful job she did for dinner (up close), but say "you notice how crowded it was? Next year, it will be at my house, it will be less stressful on you"
or your can say that now---"it will be crowded, which means more people in the way, making more stressful, and since this is our first X-mas together, I don't want you to stress out, it's a season to enjoy our family and each other..."
this shows that you care, yet you get point across, but at the same time showing compassion, want, and desire for her...sometimes a shot doesn't have to be fired to win a war.