My son won’t eat the roast, but he will eat all the melon starter(excluding the prosciutto), all the veg and he’ll have a dessert. I’ll also bring him some fritters that I’ll put on the table and serve him like they’ve come from all the food table.
I recommend a sectioned plate so food can't touch - that way if she becomes interested in your dinners she can try some without it contaminating her own food or even a side plate. I don't know how you serve Christmas dinner - we tend to carve meat onto plates but then everything else is on the table for people to help themselves. You can always put an element of her meal in a little bowl for her to serve herself just like the adults. Also we always try do place settings (by this I mean, a christmassy plate mat, a glass, cracker, napkin) if she has one as well it will help her feel included.
My little boy doesn’t like a lot of roast things - like potatoes (roasted or mashed) he doesn’t eat a lot of and probably wouldn’t eat the Turkey. But he does like things like a sausages, peas and carrots. As we’ll probably have pigs in blankets and veggies too, there is enough similar things to make it feel like there is more crossover with our food than there actually is!