Thank you Susan for making some bells go off in my head!!!
When we took prisoners, the "golden rule" is that they have to be fed the same food from the same pots as our crew. The problem quickly arose that they could not physically "handle" our food as it was too rich for what their systems were used to. We had to then feed them the beans and rice that their systems were accustomed to.
This may be "part" of DD2's problem with the tummy. It sounds like she has maybe gotten something her system was overpowered by. Monitor her foods and see if there is any cause and effect evidence to substantiate this possibility.