There was an interesting article in the Coeliac Society Magazine a couple of years ago that was about re-introducing gluten for a challenge - but I think it was more about the reaction to gluten. It was found that immediate reactions were more severe early on in the challenge, but there was a slight improvement later on.
Has she been officially diagnosed with fructose issues? If so, then I guess introducing wheat back into the diet would be a no-no? If she can have wheat - then I might consider giving her 2 pieces of bread at night, so she can hopefully sleep when her body will be reacting the most.
There is a risk that your child will refuse to eat the food - as they might be aware that it makes them feel sick, so it can be difficult to feed them gluten foods.
Before my DD was diagnosed, she had stopped eating a lot of foods. I finally found that she would eat french toast - so that way she was still eating gluten before her biopsy.
It's really difficult as a parent to knowingly feed your child food that could be making them very sick - so you just have to keep reminding yourself that it will be worth it in the end - you don't really want to do the challenge for 3 weeks then bail out.
Just be prepared for a decline in behaviour, sleeping, eating and health, and take it easy on yourself and your child. My DD had no energy, so I couldn't even take her shopping as she struggled with walking around the supermarket!
We also had a lot of sleepless nights.
It was worth it in the end, to get the official diagnosis.