She might have died from mites...

[Bird biz]

Treated my little Golden Egyptian fayoumis Bantam for mites as she was pecking at her feathers. I treated her with Garden and Poultry dust, but a few days ago she appeared cold and just sat in one place. I brought her into a cage near a heater and kept a close eye on her. She soon lost her appetite and became very week. Saddly she passes last night. She was about 4 months old. The only other symptoms she had was that she appeared to molt and the shafts of her feathers were cover with a white coating. No one in Denver seems to know much about chickens. They have only this year allowed residents to have them. I have gotten lots of responces about what could have been wrong, it's a mystery because the other five appear well.

 

[zurcherpoultry]

I wouldn't keep mites out of the question. We have white crested black polish which are notorious for mites. We got to the point with one where she died from a mite infection before we noticed it. A lot of times you won't notice the mites until they are gone. I would treat the whole flock, chances are they probably have them too.

Sorry for your loss!