Sorry for your loss. Welcome to BYC. It could that she was attacked. Was there any sign of molting? Did you examine her body for marks or bleeding? Hawks, dogs, raccoons, or even one of the other chickens could be suspect. We also have foxes and bobcats here, but those would take the body away. If you want to get a diagnosis if she was sick, your state vet could perform a necropsy. But keep the body cold in a cooler, but not frozen. Here is a list of state vets:
https://www.metzerfarms.com/poultry-labs.html
https://www.metzerfarms.com/poultry-labs.html