my hen ate too much hey and became compacted
Welcome to BYC. Are you sure that she wasn't attacked by a predator? Some will attack the crop or take the head off. Weasels, mink, opossums, raccoons, dogs, cats, owls, hawks, foxes and coyotes, are all chicken predators. Long grasses, hay and straw can cause impacted crop. Make sure that your chickens have access to feed at all times they are awake. Sorry for your loss.