I agree that you will have more information from the folks on the DISabilities FOrum, but also agree that Disney Chefs will try very hard to provide safe food for your wife. When you check in uyou wil be asked about allergies, or concerns, and again when your server arrives. The Chef will speak to your wife and if at all possible will help.
My DGD had a dairy and egg allergy sp when we were at Cape May for dinner the CHef walked through the buffet to show my DSIL what was safe for her, however there were no items on teh dessert table she could have. No problem, she rarely had anything other than sorbet ot tofuttie, and we sould get her something later if she wanted a sweet. The Chef showed up at our table during dessert with treats, including cooKids and those crazy popsbcle things the kids enjoy. Now I know your wife's concerns are much more serious than Kady's, but if they accomodate a child who really was okay without a dessert, I cannot imagine that your wife's meal would be neglected.