If the blood test is negative, it doesn't necessarily mean that wheat/gluten isn't a problem. There is such a thing as a false negative test - they are not 100% foolproof, although I think they are much improved recently. But it could be that although she is not coeliac, she cannot tolerate wheat/gluten. If that is the case then you could try eliminating it from her diet anyway to see if it makes a difference.
There is a massive range of gluten free foods available now. All the major supermarkets do their own range - bread, biscuits, pasta, cereals, gravy, stuffing, naan bread, pitta bread, pizza, sausages, fishfingers! They are a bit more expensive (if you are a properly diagnosed coeliac, you get quite a lot of dry goods - pasta, bread etc - on prescription which is really helpful, particularly for a child). But your DD would definitely be able to continue eating bread and biscuits .
If this is her staple diet though, then it does sound like this could be the problem. It becomes a bit of a vicious circle - what she eats makes her uncomfortable and gives her tummy ache, so she doesn't want to eat anything else. Certainly with my DD, her eating habits improved dramatically once she was diagnosed and wasn't 'scared' of eating any more.
Hope this is helpful and not too much of a ramble . Feel free to ask any other questions.