You might want to visit the DISabilities board. Food allergies are handled very well at WDW. The chefs at the TS restaurants are great about finding something for you to eat and have a lot allergy friendly foods available. They are also very conscious of cross contamination. With as many issues as your friend is dealing with, it would probably be worth it to call the restaurant ahead of time. Disney dining can provide you with direct numbers to the restaurants.
As for CS restaurants, they aren't able to be as accomodating, but ingredient listings are available when you are ordering. Also, there is a woman at Disney named, I believe, Brenda Bennett, who can provide you with ingredient listings for CS restaurants and park snacks before your trip. Her contact information is available on the DISabilities board. I contacted her last summer about my DD's allergy and dietary restrictions and she responded very promptly.