How about I'm going to ask that my MIL not make us engage in a religious ritual as I host Christmas Dinner.
What is it about the ritual that bothers you?
She keeps asking us to do things we don't want to do because of her religion.
I can see how imposing her beliefs on you would be annoying. It's good that you you're going to talk to her about it. Maybe you could make a compromise: whoever's hosting decides what religious rituals are or are not held.
If she wants to have a religious ritual, she can do it at her house. I'm not putting up with her there.
It's good that you are going to stand up for what you believe. No one should force you to participate in a ritual that is not apart of your belief system. Asking your mother-in-law to respect how you feel is the right thing to do.