M.B.
Your daughter's symptoms are identical to those of both my sons (including the teeth problems) who weren't diagnosed with Celiac until they were 8 and 11. I ended up using enterolab as it's a non-invasive test that can be done at home:
www.enterolab.com
It's also very important for you to be aware that if her teeth problems are with her baby teeth, then YOU also need to be tested because the enamel defect on the baby teeth is due to the nutritional deficiencies of the an undiagnosed celiac mother (like myself) because the enamel is formed before the baby is born.
And, yes the biopsy is the current gold standard for CD, but most docs won't run it if the blood tests aren't positive and for some folks, those can have false negatives (like myself). So, if you do go the conventional route and the results are negative, I would suggest the enterolab test before going on the diet. You will, unfortunately, do your daughter a dis-service by not getting the positive test results (or at least knowing she has the genes that pre-dispose one to CD) before starting the GF diet for several reasons:
1. When she's older, she's not likely to stick to the diet without you being able to point to the test results (I know this from experience with my now 14 year old).
2. Even if you get positive results on the GF diet, if she later has other GI issues, some GI doctors would require that she go on a gluten challenge later to get the diagnosis. That is cruel in my opinion, but still done by many folks.
3. It will also be harder for you to convince yourself to keep her on a 100% GF diet (which can be difficult) if she does do well on the diet. It's important to have the results to re-enforce even to a concerned mother, that the problem is real.
I wish you well and feel free to contact me if you have further questions.