Moulting or plucking?

For the last few days the coop has been covered in white feathers, at first I just presumed one of my old girls was moulting but now I am wondering if she or one of the others is plucking her as her back is getting bald!

I haven't seen any plucking her as she is top bird currently but she is coming up for 4 I think now. They have had 2 new birds introduced in the last few weeks and one is a cockerel so could that have affected her?
It's too cold to be bald!

Some hens do drop their feathers all at once and have to live with the 'oven ready' look for a little while. She will soon look gorgeous with her lovely new feather coat on. 

Ok thanks, in the 4 years we have had chooks this is the first time any of them have moulted! She now has a huge bald stripe down her back!
I did wonder if she was a little stressed since the 2 new chicks, one of which was a cockerel, moved in with them. But they have gone to their new home today so maybe if she was stressed she will feel a bit better

You would have though they would wait until it was warm until they moulted!