I am coeliac, had it since 1982. True gluten-free people will take their own food, the mantra being, if in doubt ( that it's gluten-free) leave it out. Gluten is poison for us. Stand your ground, she wants to do it, let her, tell her, ok, bring your own that way you'll be 100% safe and sure there's no gluten. She sounds like a right diva. Don't dance to her tune, do your thing. If she asks, point out what's gf and what isn't. Has she even heard of cross contamination.? Hypochondriacs like this make my blood boil. I and thousands of others have no choice, so, shrug your shoulders and let her get on with it. All of it. Leave her to stew in her own juice. I'd love her to suffer the side effects of getting ZAPPED by gluten, it lasts anything up to or longer than 6 weeks and is most unpleasant. Shake your head, tell her to do one.