Welcome To BYC @Maryb Heisner :frow
Could have been Sinusitis, the OP has not been on since the thread started a couple of months ago, hopefully the problem has resolved by now.
Is it hot or dusty in the coop?
Does the coop smell like ammonia?
Video her breathing/having difficulties so we can see what she's doing.
Upload video to YouTube and provide a link.