From what I understand there are many false negatives with Celiac Disease, but false positive is rare. My children (25, 16, 14) all have negative tTG IgA's, but all have various symptoms related to Celiac. Two of three are currently GF and showing improvement in their symptoms.
I understand it would be extremely difficult to go gluten free for a 13 year old if there doesn't seem to be a reason, but if she is Celiac it seems prudent to start now to forego potentially severe health problems in the future.
Was she tested by someone that specializes in Celiac cases? Did she have iron, ferritin, Vitamin B, D, K tested?
Fibromyalgia 10/27/09 & Celiac 3/26/09
Med/Supplements: Flexeril at bedtime; Multi-Vitamin, B, D, Calcium, Magnesium, Fish Oil, Probiotic -- Trying Malic/Acid, CoQ10
Still a mystery - heat/humidity intolerance