help please

[NONA BUTNER]

Healthy 1 1/2 yo hen dies. There was egg- lots of egg contents on her behind feathers but no shell or membrain-some egg in nest as well. No egg in her vent. I cleaned her up and returned her to the small flock. She was weak and wobbly and died later in the day. Her crop is full and mushy. What in the world could have happened to this beautiful strong and healthy chicken?? The other five hens seem well. I am heart broken!.