chick attacked

On Sunday for some reason some of our hens took a dislike to one of our 9-10 week old chicks, they've all been mixing with no problems for the last 2 weeks. We found her laying very still in a corner of the run with most of our hens surrounding her. On picking her up I feared the worse and was shocked to see that they had pulled every feather from her back, it looked so so sore, fortunately the skin appeared unbroken. We brought her home, washed her with anti-septic then applied the purple spray. After a few hours at home we put her back in a seperate pen with mum and her sibling, she now appears to be feeding and drinking with no problems. Now a question for the more expierenced hen keepers, has anyone had a similar situation, do you think her feathers will regrow?  or will my wife have to knit a little cardy for her !! 

thanks for your reply Joyful, no mites etc, it was our other hens that took a dislike to her, anyhow she's feeding well so hopefully will be ok. Re-introducing her to her attackers will be another matter though !

No Cockerels allowed on our allotments, we have 8 hybrid hens & 2 bantams. The chick thankfully appears fine now, I just have to try and catch her to check her back again, fingers crossed the feathers will regrow as it's completely bare at the moment.