Your DD is 'lucky' to be diagnosed at 17. I was diagnosed last year at 60! I have the classic dental symptoms; my enamel is not too bad, but I have translucent and mottled teeth and horizontal ridges, my teeth are prone to breaking, and the hours I have spent in dental chairs and the amount of novocaine that I've been injected with are beyond counting.
To get the dental symptoms, you have to have had active coeliac disease when the adult teeth are forming at the ages of between about 2 and 7.
I don't think dentists are particularly clued up about this. When I was 22 I moved away from home for my first job, and ended up seeing a late 20s dentist who had his surgery decorated with all the certificates for the prizes he had won at dental school -- there were a lot. He did ask me whether I had had a serious childhood illness at a young age, which I denied in ignorance, having checked with my DM in case there was something when I was too young to remember. While it was 40 years ago, and understanding has moved on, even he, though, didn't go so far as to suggest a cause.
After diagnosis, I tried to point out my defects and their cause to my current dentist, whom I would guess is about 30, but he wasn't really taking anything on board.