Mystery illness?

Hi,

I recently had a hen die of a mysterious illness. At least I assume that's what she died of. She had reddish brown flat, irregular shaped scabs that spread over her comb and wattles and she seemed tired and didn't stay with the other girls, spent lots of time laying down. Then her tail went down instead of the normal cocked up tail attitude, and her "friends' shunned and bullied her. Final evening she was breathing heavily and refused food and in the morning she was dead. All this went down over 4 days from the first sign of the scabs, rash. I Googled the heck out of it and Fowl pox was the closest thing-but there were NO light coloured bumps or blisters before the scabs and the scabs were much flatter than any of the images. Also the internet suggest fowl pox is rarely fatal and 5 days before she was happy, shiny, laying, active and eating well. I couldn't find out if they can have wet and dry fowl pox simultaneously? But there are different viruses. They have been roaming the back yard lately and hanging out under the wild bird feeder-so potential exposure to pathogens transmitted by wild birds? Some neighbor's cat predator stress lately too. Any ideas what this might have been? I didn't take any pics unfortunately.

So far everyone else is fine-2 weeks out now. I did power wash, disinfect and repaint their house.

Cheers,