stripped back

 When i put my garden girls to bed tonite I noticed that Sheila's back has been stripped of feathers (she is black araucana)its not bleeding but there is a patch of about6 inches long and 3 wide that has been plucked completely. it was not like that when i had coffee with them at about 5 this afternoon. i can only assume that she submitted to one or more of them and they were vigourous about it.  she is not dominant - nor is she bottom of pecking order but i cannot let her go in with them tomorro - she will have to be confined in a run within the wir.  has this happenned to anyone slse's girls lucyoux

I noticed one of mine has a bald bit when her crop swells up (probably normal) but there doesn't seem to be any cannibalism going on (yet)
I'm dreading their first full moult which is due in a couple of months!!!
Do they all rush round pecking at each other?
Sounds like your girl has been treaded? How else can they reach her back? (unless they do it when she's lying down I suppose.......)

thanks for your replies - i havent got a cockerel so no one to tread her - and sh'e not moulting as i noticed some of surrounding feathers have been nipped off close to her skin. I havent noticed them pecking each other but i am at work most of the day so plenty of time to do it when im not watching them. I did have a feather pecker a month or so ago but not been a problem for a while (or so i thought)