I know it's been a while since you posted that your daughter's blood test for celiac was negative, but I wanted to remind you that the gold standard for diagnosing celiac is a small intestine biopsy - sometimes the serology is negative and biopsy is positive. Also, there is a primary immune deficiency disease called hypogammaglobulinemia - most people with this deficiency have hypogammaglobulinemic sprue, which acts much like celiac, even looks like celiac on biopsy, and people frequently improve on a GF diet - but the blood work for celiac disease is always negative in this particular sprue. The gastrointestinal tract is the largest organ to regulate our immune systems - just because one has GI symptoms, that doesn't mean it didn't start somewhere else.

I wish you good luck in tracking down the problem... ~~Allie