Very sorry for your loss. She sounded like she was very weak from the trampling, or she may have been weak from the start. Coccidiosis can be common in chicks 3 weeks and up until they develop a resistance to it as chicks with normal immunity do. Occasionally a weaker chicken may get it too. Some treat chickens prophylacticly with Corid in a low dose for 5 days to help prevent outbreaks, but that is probably more common in large breeders or those who have had an outbreak before. It helps to keep the Corid liquid around, just in case you see a weak puffed up chicken or blood in poops. Coccidiosis does not always cause bloody poops though.
