You could try using creamed corn instead of cheese on tacos. It gives that additional texture and flavor you're missing when you don't use cheese. I've been doing this for a few years now as I've worked to cut down on the amount of dairy I consume, and it's delicious.
My company does a big lunch for everyone for Thanksgiving and Christmas. I am normally completely open and happy to talk about my celiac, but I HATE these lunches. I always have to sit with people I didn't know well because everyone comes down to the cafeteria that day, and when I say food allergies, I get the question "you're allergic to turkey??" more times than I care to count. So now I treat it as a social hour. I pretend I've already eaten and jump from table to table with a drink in hand socializing and saying hi to everyone. No one asks questions if you're not eating because they assume you've already finished, but everyone asks questions if you're eating something different.
You could have her search around for a doctor that will diagnose her with celiac or gluten intolerance due to her reaction to eating it. I never had positive blood work, and my doctor (and the few doctors I've had since) was perfectly fine with a diagnosis based on dietary response. I'll admit, I try to find someone younger, someone who may be more up on the current celiac research and open to less traditional methods of diagnosis.