Hi, I'm Ceoliac and so have to be gluten free. I've lived in Fethiye for over 5 years and it's perfectly possible to cope. Dairy products are not usually a problem for Ceoliacs or those who must be gluten free. As others have said the large supermarkets do have a small gluten free section, if you are catering at home you can get Glutensiz flour (un) from Migros or Kipa and they also do some biscuits and little chocolate cupcakes by Pronot. Quite a lot of Turkish foods have corn (misir) starch rather than wheat (bulgar) starch but you do need to check the ingredients
My advice would be to avoid sauces, mashed potatoes and gravy if eating out as they are generally packet jobs and you don't know what's in them. If your friend is happy with plain grilled steak or chicken and veggies, salads etc., no problem.
If you tell the staff that bulgar and flour (un) is a problem you should be OK. Hope your friends enjoy their holiday.