Kate-- have they tested her for Shigella or e-coli? Sometimes that can cause children to be sick a while. I know you said she stayed in a home daycare, but that sort of stuff can run rampant in day cares.

Also, I thought of mono. Kids that young usually aren't as susceptible to it, but it can present in different ways.

Maybe something else is going on with her stomach, like celiac disease or even a food allergy.

Keep us updated!

Jess