Mite??

Hello,

Just wondering whether anyone could help me. I am relatively new to chicken keeping and have noticed that one of my hens has lost some base feathers.

On further inspection it appears that the hens bottom looks quite red and sore, and I have also noticed that the chicken appears to have diarrhea. Does anybody know what could be causing this? I'm not sure if the two are linked together and was wondering whether the soreness was being caused by mite - I couldn't see any, but have dusted the chicken liberally. I presume that the loss of feathers is caused by irritation.

All of my other hens appear fine!

Do you know if she has been wormed? also have you seen any mites on her?