@tamsin So sorry to hear this. Working around gluten is an absolute pain and I sympathize with what your daughter is going through

So, first things first, if the entire house isn't gluten free, you can't guarantee cross contamination isn't happening. Especially if she is really sensitive, which it sounds like she is. I've been GF for almost 20 years now and I've had some issues with getting glutened just by being around flour. Not even (consciously) eating it. Just by being in a house (or a supermarket or a bakery) where gluten is present. Touching wheat flour gives me hives and I've gotten glutened by eating at people's houses where bread is present, so the cross contamination concern is top of mind when I read your post. I've learned how to adapt and I understand that I probably will get glutened when eating out or with friends. I'm not as sensitive as a lot of people are, so I can live with the occasional flare up, but it is something to keep in mind for very sensitive eaters

Even some certified gluten free foods are processed on equipment that handle wheat, or it's hidden in ingredients like matodextrin. It's good to check upstream manufacturing especially with things like oats which are frequently a source of contamination. Definitely do your due diligence and do some tests. It'll suck, but knowing which foods are totally safe is key to reducing long term exposure. Some gluten free bread replacements actually cause more problems than they fix, so it's worth cutting replacements out until you know what the cause is

Lastly, she may have multiple food sensitivities. Some non-gluten foods have proteins that cross react with gluten. Corn, rice, and oats, ironically, are sometimes cross reactive with gluten antibodies. What I did to help find my safe foods was literally just stop eating any processed food and any grains. It was steamed veggies, fresh fruit, and meat for a few weeks until I could isolate the things that set me off. You're probably already doing this or have been advisted to do so, so I won't go in depth on it. However, I was surprised to learn that this is how some people discovered they had sensitivity to unrelated foods. Sometimes that goes away once you reduce your inflammatory response, sometimes not