The AGA tests are older and were replaced by the DGP tests, but the AGA tests are still good! An IGA deficency test will help determine if the TTG and AGA IGA results are accurrate. It is a test control. Also, many celiacs are IGA deficient too. In your case, your child is NOT IGA deficient because she had that AGA IGA test was positive. Sorry, for not re-reading your first post.
Personally, I had only one positive on the DGP IGA and the rest of my celiac blood panel -- even the TTGs were negative, yet I had severe intestinal damage. Why? My doctors are puzzled because usually kids can be negative on the TTG tests and positive on the DGP or AGA tests. I am over 50! So, do not let the lack of a positive TTG Test throw you off to finding a correct diagnosis. Please search/Google "Negative TTG positve AGA celiac disease" and you will find many studies to support this.
I hope this helps!