A huge warning - I am mostly vegetarian (because meat is expensive as fuck) and in a lot of vegan circles.
While I think your idea is commendable, also know what kind of vegan she is.
Vegans can literally be salad eaters. Or only eat vegan burgers/nuggets. Or they eat a bunch of soups and noodles.
At one party, the host made this beautiful vegan salad with chickpeas. The vegan looked at it and was like, "ew." And then ate all the potato chips.
It'll be easier if you both make the meal. But if you surprise her, it might not go the way you think it will.
It's a really stupid idea to upset the military while they're on active duty. Well, America might get their first military uprising.