When I was interested in this one girl and found out she was vegan a friend teased me by saying "I should tell her you may be vegan but you'll still take QMan's sausage right?"
Ask her on how she feels about meat most vegans and vegetarians I know don't care if I eat meat. I don't know if your girl will mind. She shouldn't though since she can't force you to change your eating habits.
Coming from a vegan, it always makes me a little sad when people around me order non-vegan food because my mind always pictures how they died and then I start thinking about how terrible of a life they had, and so on. In general, people eating meat makes me sad, but I never comment on it. I get sad on the inside, that's all lol. We're also very used to it and we accept that most people are not vegan, so it's a non-issue. Order what you want, she won't like it, but she'll accept it and most likely won't say anything.