On vegetables some are more of a trigger then others and the same goes for fruits. Fruits high in frutose can be a problem. Vegtables with a high acidty can be problematic for some people.
"Also she is better on the days that she has had no fruits or vegetables "
Because they can be triggers and these can be individual to the person.
"weight loss"
That is an issue, if its weight loss and she is still eating enough food as well as how fast and how much weight.
Or if she doesn't eat enough food, because foods=pain?
We also totally understand your concern as a mother. As some one who had this at a young age and with the help of others here we will try to help you out and this is important, there are things to do and try that will make her better. Not all of them will make total sense at first, but things can be done for sure. A big part of that is education and questions and all questions are no problem.