I would ask if there's anything she doesn't like.
As a vegetarian, if I was being fussy, I'd say no to things like leek mornay/cauliflower cheese or butternut anything as my centrepiece because it's another veg. It needs to be something with protein.
I don't really like pastry and anything wellington is just veg or mushrooms in pastry. Same goes for pies and tarts.
Quorn makes my sibling sick, some of it does me.
Nut roast is good in theory but some of them are a bit like bird food. Something like a nut and bean roast is better. The Hairy Biker roast looks good but cashew nuts will make me throw up.
Fake roasts vary. I like the Plant Chef ones from Tesco. I'm just one vegetarian, others might not like them.
A big no-no for me is the centre-piece not matching the rest of the plate. For example, something like Christmas dinner with falafels/tagine/a big blob of curry on it.
I'd make more than one portion of the veggie dish. Others might want to try it.
Avoid cross-contamination like using the same serving tools. Check that the foods you buy are marked 'Suitable for vegetarians'
Puddings like panna cotta, mousse, cheesecake etc are often not vegetarian.
Cheese will be labelled as vegetarians if it is.
Wines and other alcoholic drinks are often not vegetarian.
(Yes I'm fussy but I'd be fine with a plate of veg especially with lots of roast potatoes)🎄