Vent Blow out/ Dead bird/ Cannibalism

[CWDancer]

I was away at a Wedding Saturday and when I came home and checked on my girls about 5 PM all looked fine. Refreshed their water and feed and went inside to make supper. After supper (about 8PM) I went out to close them in for the night. I found one of my girls dead in the coop which is very secure (18 inches down with sheet metal than rocks, than dirt to prevent predators from getting in). I picked her up only to discover she was eaten around her vent and about 12 inches of entrails hanging out. Vent looked red and swollen. GROSS, GROSS, GROSS!!!! I have never had an issue like this before. Everyone seems fine now, I checked for any possible predator entry attempts and found nothing. Should I be worried about cannibalism? Or was this just a case of picking at red when they saw it?
I had the dead bird burned to avoid attracting predators from smelling it and coming to find it.
Thanks
Diane