Maybe had a Pre existing condition?
Yeah -- Political Outgroup (white, Christian, conservative ..... whatta ya got?).
That medical history evidently caused the 7 YO's application to get funneled into some kind of code bug in the federal exchange software. It definitely isn't disqualifying in a legal sense as one of the big points of PP&ACA is to mandate acceptance of applicants with pre-existing conditions. This is why the staff she talked to on the phone were uniformly puzzled about the situation.
I wonder if this would have happened if Alabama had been running a state exchange. I have not heard of any similar problems on my own state's exchange. There have been glitches such as incorrect subsidy calculations, but not outright erroneous rejection for either a subsidized exchange plan or state Medicaid to the best of my knowledge. However, mixed commercial and government coverage-type applications are quite complex and the required code must reflect this complexity if it is to process the apps correctly.