What Causes Nausea And Vomiting After Eating?

What would cause a person to be nauseated and even throw up with almost all foods? When she was about 8 to 10 years old, she was found tested and found highly allergic to carrots. I was also told that she would not do well on a soy or wheat diet. As she gets older, more fresh vegetables and fruits would make her mouth itch or swell. Food cooked with tomato sauce can cause her to throw up for 2 to 3 days. The only foods that seem ok, is white rice and plain pasta. Mind you, because she has stayed away from the majority of fresh foods, retesting her did not show her positively allergic to any food, so the allergist treated her with disbelief. Steph is 26 years old and I am her mother, Bev.