A simple reason why any celiac would get worse on gluten free diet would be a replacement of gluten foods with foods that you are still intolerant of, even more intolerant than gluten, like corn, or oats or rice.
Being celiac does not automatically mean that you can tolerate corn or rice or oats or whatever else you are eating.
There are people who are sensitive to wheat and gluten, but are even more sensitive to rice. Rare, but not impossible.