I have celiac, and this person went about this issue in entirely the wrong way. I suspect that she may be really freaked out about a new diagnosis and not handling that well, which I totally get. Going gluten free is really life-changing and a huge deal and a big pain in the ass until you get the hang of it. She also may have already had bad experiences with people being unwilling to try to work with her diet at all. My paternal extended family is such an ass about gluten free; both my mom and I have celiac, and yet they refuse to even try at all to understand or accommodate in any way, and I can tell you right now that packing your food to eat at Christmas while everybody chows down on some awesome shit is very, very sad. It is so alienating how much you get left out of--the potluck at work, just blithely accepting dinner invitations to people's houses, even going out to eat means you have to choose a restaurant where you can get a gluten free meal. So I suspect that she is still in the anger portion of the grief of being diagnosed with this kind of disease.

What she should have done is tell them that she's diagnosed with this disease, ask them what they're going to make, and then offer some suggestions for ways they could make it okay for her to eat some if not all of what they're having while realizing that she's probably going to have to bring her own food. She could say, "Ooooh, do you mind not putting croutons on the salad and serving it in a glass bowl? I'll bring a dressing I know is gluten free." Etc.

I am so lucky that I have friends who invite me to their houses and serve gluten free meals to me and that when we host they bring gluten free side dishes. I would be lost without them. But I never demanded anything from them; they volunteered and took the effort to do so.