As a fellow coeliac, I can understand why that would stress and upset you. I have a mostly gluten free kitchen too other than bread and treats for the rest of my non coeliac family. I do find people need educating regarding coeliac disease- there isn't a sliding scale of severity as you imply, you are coeliac or you're not, regardless of your symptoms you are still having exactly the same amount of internal damage if gluten is consumed.

I do have to say, and this is just my opinion, there has to be a way of managing everybody's dietary requirements to keep everybody happy. There isn't ever going to be a fully gluten free free of contaminants place other than your home- school, friends, restaurants all pose a risk and it's about mitigating those risks without creating massive anxieties or phobias.

Obviously your situation is extreme, but I would do what I always do, roll my eyes, traipse out my full spiel and make sure they thoroughly clean down after. I'm actually going for ESH