Hmm...now I'm not sure what to think. It is too late for necropsy- she is buried. I appreciate the responses. It is very traumatizing to go out to the run and find your young chicken dead of no apparent reason.
I do try to necropsy birds who die unexpectedly, but it's hard sometimes. In the future, if you chill the body in cold water and wrap it in plastic in the frig, it can be checked a few days later if there are more deaths. Not nice to consider, but sometimes necessary.
Mary