Welcome to the forum, @Gill.brittany8, Yes, the bloodwork is confusing.   One has to be eating a sufficient amount of gluten (10 grams/day, about 5-6 slices of bread) in order for the antibody level to get high enough to be measured in the bloodstream.  If insufficient amounts of gluten are eaten, the the antibodies stay in the small intestines, hence the statement "tTG IgA may normalize in individuals with celiac disease who maintain a gluten-free diet."  The bloodwork reflects anemia.  People with anemia can have false negatives on tTg IgA tests because anemia interferes with antibody production.  Diabetes and Thiamine deficiency are other conditions that may result in false negatives.  Anemias, B12 deficiency, iron deficiency, Thiamine deficiency and gastritis are common in undiagnosed Celiac disease.    The DGP IgG antibody test should be given because your daughter is so young.  Many young people test positive on DGP IgG because their immune systems are not mature and don't produce IgA antibodies yet.  Your daughter has several alleles (genes for Celiac disease).   Your daughter needs to be checked for nutritional deficiencies.  Iron (ferritin) B12, Vitamin D, Thiamine and Vitamin A should be checked.   Were any biopsies taken during the endoscopy? Keep us posted on your progress.  

The intestinal tract can be as long as twenty-two feet long, so intestinal damage may be out of the reach of endoscopy tools.  Some people have had more success with capsule endoscopy, but this method cannot take biopsies.  

@Jack Common, It's possible that your antibiotic for giardiasis has caused thiamine deficiency.   https://hormonesmatter.com/metronidazole-toxicity-thiamine-deficiency-wernickes-encephalopathy/ And... Thiamine and benfotiamine: Focus on their therapeutic potential https://pmc.ncbi.nlm.nih.gov/articles/PMC10682628/ For clarification, the weight of your slice of bread is not equal to the amount of gluten in it.   Gluten helps form those big holes in breads, so breads like thick chewy pizza crust and artisan breads contain more gluten than cakes and cookies.  

Sorry about that link.  It was meant for a different post.   Do consider taking high dose Vitamin D in order to get your level up to around 80 nm/l quickly.   This is the level where Vitamin D can properly work like a hormone and can improve the immune system and lower inflammation.  It makes a big difference.   I took high dose Vitamin D and really improved quickly.  I ate Vitamin D supplements throughout the day like m&ms.  My body craved them.  Very strange, I know, but it worked.   Before you have surgery, you really need to improve your vitamins and minerals.  Vitamins A and D, Vitamin C and Niacin are extremely important to skin health and repair.  Without these, the body does not repair itself neatly.  I've got a scar worthy of a horror movie.  My doctors were clueless about nutritional deficiencies. A sublingual Vitamin B12 supplement will work better for boosting levels.  Tablets or liquid drops in the mouth are easily absorbed directly into the blood stream.   Do bear in mind that about half of Celiac people react to the protein in dairy, Casein, the same as they react to gluten because segments of the protein in Casein resembles segments of the protein Gluten.  Some people lose the ability to produce lactase, the enzyme that digests Lactose, the sugar in dairy, as they age.  Others lose the ability to produce lactase because the intestinal Villi become damaged during the autoimmune response against gluten, and damaged chili can't produce lactase.   Do try Benfotiamine.  It has been shown to improve gastrointestinal health and neuropathy. Keep us posted on your progress!

Thanks sending me additional links including how to test for thiamine deficiency. With regards to your first link, I wasn't diagnosed with giardiasis and I didn't take antibiotic for it. I try to generally stay away from antibiotic unless absolutely necessary as it might affect gut health. For treating phimosis, the doctor didn't give me antibiotics. I need to have a circumcision surgery which I haven't got around to schedule it.