I have a problem with food, or lack of it lol!!
I have Multiple Chemical Sensitivity and I am Gluten, Dairy and Sulfite intolerant and I have recently discovered some new food allergies after my recent skin prick test, whilst visiting my allergist..but really, the best way and most accurate way for me is to carefully keep and monitor a food diary, as skin prick tests aren't always correct, for example I think I have a problem with Walnuts, which came up fine on the recent skin prick test!! and so it just goes to show you cannot count on these tests totally. Through carefully writing down everything in my food diary (which is kept open on the kitchen table) I have recently discovered I cannot take extra virgin olive oil, which I was using two or three times a day, and just that simple discovery has meant I am now sleeping much better. This is something that the allergist couldnt possibly have picked up, and thats why a food diary is really the only way to know for sure what your daughter can safely eat.
Food is a challenge, more so at the moment, and I am eating carefully, as I usually get a reaction within an hour, and I then know to avoid that particular food in future, I wonder how quickly your daughter knows when something does not work for her...
At the moment my staple foods are Rice (the allergist initially told me I had a problem with this and I asked to be retested and it came up fine) Sweet Potatoes, Potatoes (all organic) and Quinoa. I then stick with chicken, salmon, mince, beef, all organic, and I eat a lot of organic fruit and vegetables.. Drinks are a problem at the moment and so I tend to stick with boring old water for now, but that is hardly going to be exciting for your daughter, so maybe you can make some healthy drinks for her. I think most over the counter drinks are probably going to be bad for her.
If you look on Amazon, under the brand name "Enjoy Life" you will find that they have some really good snacks which are handy to have in the house as special "treats" for your daughter.