Hi Audie! Disney World is very accommodating of special diets, and I think your fiance will be pleasantly surprised with her dining options. Most restaurants have at least one vegetarian meal on the menu, but if it doesn't appeal to your fiance, just ask the server for additional vegetarian options. 'Ohana is a meat-lovers paradise, but a delicious vegetarian meal of tofu, vegetables and rice is available upon request. Likewise, at the Hoop-Dee-Doo Revue, fried chicken and ribs are the mainstays, but vegetarians can order grilled vegetable or pasta meals instead. You'll find that all restaurants can make similar off-menu accommodations, which I've found makes Disney World a very easy place to eat for a vegetarian.
As to your where to watch the fireworks while you dine, I have a few suggestions. To view the Magic Kingdom fireworks, I'd recommend dinner at the
California Grill. This restaurant is one of the best at Walt Disney World, and it has a private outdoor viewing area where you can watch Wishes and listen to the piped-in soundtrack. The menu has several vegetarian options. (I can attest that the flatbreads, the Sonoma Goat Cheese ravioli and and the Beet Salad are all delicious!)
At Epcot, the
Rose & Crown has an outdoor patio that's a wonderful spot for viewing Illuminations while you dine. I had the Apple Stilton Salad and the Vegetarian Shepherds Pie on my last visit there and really enjoyed both of them. If you like Mexican food, consider
La Hacienda de San Angel, where the dining room has large windows facing the World Showcase Lagoon. This restaurant has a special printed vegetarian menu available upon request. I tried the Cheese Empanada entree on my visit and it was good.
Hope this helps!