Hen appears to be having difficulty breathing?

[Kiwiluff]

Went out this morning to let the chickens out of their coop and this one has been breathing strange, she has a long growling inhale then extends her neck to an opened mouth gasping exhale. (I have a short video but can't upload?) She was also the only one still roosting when I let everyone else out, and was much easier to pick up than usual and she seems lethargic.

She's a 1 year old Black Marans, doesn't appear to have lost weight recently and is the only one of 11 doing this but this morning I did notice some sneezing from two others. I have her inside in quarantine at the moment and provided food and water but so far she hasn't touched it. The coop bedding is straw and they "free range" the backyard during the day, the coop was cleaned out a few days ago but is probably due for another cleaning. There's no apparent injuries and her crop is flat and smooth. I put some probiotic/electrolytes and VetRx in everyone's water.

Any ideas?! They are pets so I'm very concerned for her

 

[Kiwiluff]

 

[Kiwiluff]

Gonna keep this updated as our illness progresses incase it helps someone else in the future or someone has any input/advice.

Yesterday morning I noticed my rooster had a ton of nasal drainage, left eye was swollen shut and his waddle was hot and swollen as well. He's been super lethargic and not eating or drinking.
Later that evening I noticed another two hens with a lot of sneezing, nasal drainage and crackly, wheezy breathing. This evening I found yet another hen with crackle breathing, lethargy and swelling to the left eye. Whatever this is seems to be spreading quickly to the entire flock despite quarantine efforts.

I'm fortunate enough to live near a vet school so I took the rooster in this morning since he seems the most ill. They cleaned out his eye and said it was full of pus and offered a testing panel for infectious disease and provided antibiotics for him.

 

[Kiwiluff]

Another update: Swabs are back from the lab and he tested negative for everything they checked. I was really shocked!

All of my flock ended up infected with whatever it was. Wheezing, nasal drainage, sneezing, swollen eyes and faces. No casualties! The antibiotics got big boy back on his feet very quickly and he's back to being a jerk, the rest of the birds did not receive any antibiotics until a couple of days ago I bought some from chewy.com to put in their water for a couple days and they started to recover on their own. One girl still seems a little unwell but not nearly as bad as we started.