my hen died with few symptoms need help for answer please

My approx. 3 year old speckled Sussex hen was found dead in the pen yesterday morning. She was dead for awhile because she was already stiff as a board and cold. Where she had been in the coop the night before there was a large amount of thickish white loose liquidy poop. just before night time she seemed a little slow and unenthusiastic but nothing major.

I pulled her back from a bad bout of sour crop last year and she was much sicker then so I wasn't worried much about her that night.

Earlier in the day she didn't run for her mealworms but she was out in the yard with the rest of the girls running around. What could have happened? They were wormed early in the spring. They have anything a chicken could want. This hen was picked on frequently by one of the others but she had buddies too and knew how to evade the bully. I did not see any bleeding but her face was very reddish purple. Can anyone help? Did I miss something I could have done for her?