labored breathing (like a cold), discolored crop, and being pecked at

I have a black sex link just over a year old. great layer. has always had a small crop, not very bright, but now seems to seem dirty (always somewhat grey on top), black spots (but not like a pox, just discolored).

Just today, another hen (the alpha) has started pecking at her and it appears that she is missing feathers around her neck from pecking...the pecking hen is not letting her eat.

She seems to also have some labored breathing - like she has had a cold for a few days. We have seperated, but the sick hen really wants to go back in the pen. They were all out in the yard earlier acting fine. No other sign of illness. We just want to be preventative.

All the hens typically get along and have been together.

sudden temp changes for the past few nights (frost warnings)
coop above ground
three hens
layer pellets
other treats/sometimes free ranged
wood chip bedding/DE

Urgent? Just let is take its course? thanks for any advice
Joe

 

YES...sorry, I do mean her comb. It has never been bright red like her sister hens. or as large. always kinda greyish red. And has had splotches of black - like I said earlier, never a new pox mark or growth.

She has been separated. Is eating/drinking well, no discolored poo. no runny nose. and happily ran around the yard again until I picked her up to recage her; then she started the wheezing again.

bad feed?? it all seems ok...I'm cleaning out the coop and changing food today.

still puzzled by no more symptoms. (which may be a good thing!)