As a vegetarian (by ethical choice, not medical necessity), I do my best not to lose sight of the simple fact that
I'm the problem here. When I walk into a steakhouse with my carnivorous wife, they're helping me out by finding something to put in my stomach. If I'm on a camping trip, I'm bringing my own food, or doing my best to make it fair to folks who are helping me out. And if I'm visiting for dinner, I try to make it clear that I'm happy to scavenge sides, you don't need to do something special for me. Because, again, my self-made diet choices are not your problem, but mine.
Celiac is real, folks who have it should be cut a break, and in my experience, folks who actually cannot eat gluten are just trying to make things work, rather than being a dick about it.
But deeply screw people like this lady who make a voluntary diet choice who use it as an excuse to bully others and make people cater to them. They trivialize people's actual medical needs, breed a culture of "Yeah, sure lady, there's no gluten", work against whatever cause they're in favor of, and largely, they're why we can't have nice things.