I'm a lacto-ovo vegetarian and my husband eats meat. Virtually every table service and full counter service restaurant has at least one vegetarian entree. You will see a lot of veggie burgers at counter service places (bland Boca burgers) that can be dressed up a bit with lettuce, tomato, onion, cheese, etc.
My absolute favorite vegetarian meal right now is the root vegetable pot pie at the Rose and Crown (UK pavillion in Epcot). It's absolutely delicious. Their coiunter service fish-and-chips has vegetarian french fries that are fried in a separate fryer from the fish. I rarely eat french fries out in the rest of the world because they're usually fried in the same fryer with chicken, fish, etc., so this is a big treat!
The veggie burger at the Rainforest Cafe in the Animal Kingdom is homemade (not a Boca burger!) and excellent.
The vegetarian combo at the Mexico pavillion table service restaurant is very good if it is served hot (and so-so if not hot). You didn't ask about the atmosphere

, but the Mexico table service restaurant has the most romantic atmosphere of anyplace I've ever eaten and I highly recommend the experience!
I also like the mac-and-cheese at Chefs de France in Epcot and the mozzarella etc. sandwich at the Main Street Bakery in the Magic Kingdom.
I've heard that the resort restaurants have better food than the park restaurants, but DH and I can't tear ourselves away from the parks long enogh to find out if this is true.

We've stayed at Pop many times and we always eat breakfast there. Your wife will be able to get a vegetarian omelet, oatmeal, fresh fruit, pastries, etc. The breakfast potatoes look good but don't taste particularly good.
Have a wonderful time!