hen losing backside feathers, skin red?

[Nyxish]

from a friend:

"Trill has lost many feathers around her tail/rear end. The exposed skin is red on her back end, but around her tail looks normal. Do you have any ideas what might cause this? Or what I might do? Do you think it could be something like a yeast infection? If so, what can I get to treat it? She doesn't seem distressed about it, and I haven't seen her scratching or pecking herself. I haven't seen the other two pecking at her either. "


i've suggested isolating Trill if possible and asked about droppings, but that was 5 min ago.

background: Trill is a barred rock i raised for my friend Jill. Came in a shipped order. Knock on wood, all my girls (minus one, rip Bree) from that order are healthy, happy and spoiled. Trill is... a year old in June i think. Trill and Maizie (a buff orp) have been living with Jill's Rosie (a reddish hen-mutt, and a couple years older) since... last September i think. Everyone else seems healthy. No egg-laying difficulties that Jill has noticed.


Mites?
Picked on?
Where do i look?

 

[junebuggena]

Does a rooster have access to her? If it's a feather picker, the feather picker needs more protein add to her diet. It couldn't hurt to treat for mites and lice, but all the birds and the coop need treated for it to be effective. If the feather loss is significant, she might not grow back the feathers until after a molt.

 

[Nyxish]

No rooster at all. Just the 3 hens.

 

[junebuggena]

Then it's most likely lice/mites or a feather picker.