Not a vegetarian, but I do enjoy veggie meals.
Try Tusker House in the AK - they have great veggie starters and side dishes to make a full meal.
We don't usually eat in the DHS, but I looked thru the menus and Hollywood & Vine has some dishes at dinner, the eggplant napolean at Mama Melrose's is great (if they still have it on the menu) as well as their salad, soup, flatbreads & fish dishes (if she eats fish). In FW in EPCOT there is the Electric Umbrella and the veggie wrap, Sunshine Seasons has nice offerings as well. Heading to the World Showcase you have Le Cellier, veggie burger & wrap at the Liberty Inn, Nine Dragons has a veggie salad, stir fry and fried rice. At Restaurant Marrakesh they have salads, veggie couscous and seafood offerings.At Yakitori House they have miso soup, salad and california rolls, udon noodles and tempura shrimp (agagin, if she eats fish).
In the MK you have Cosmic Ray's and the veggie wrap, veggie burger and fries as well as yogurt (if she eats dairy), Crystal Palace is a good bet since it's a buffet and there are plenty of veggie dishes, pasta and fish.
The Liberty Tree Tavern has soup, veggie pot pie at lunch as well as fish.
Pecos Bill's has a veggie burger and fries, the Plaza Restaurant has tuna salad or a veggie sandwich (roasted veggies), Tony's Town Square has both lunch & dinner items available. You can also get veggie foods at the hotel restaurants/snackbars/food courts AND any chef will be more than helpful if there is nothing on the menu to meet her needs.
Why not pick out a few restaurants and go over the menus with the family and see what you find to fit everyone' sliking. Have a great trip!! :wave: