A confusing case: can anyone give some insight?

Black Austrolorp, just under 30 weeks. Started laying a month ago. About 3 months ago, I started noticing her holding her mouth open at night time on the roost. Not every night but maybe 2-3 nights a week. I thought about quarantine but the next morning she came running out, eating and drinking fine. We've carried on like this for the last few months but today and yesterday got up to 95 degrees and she seemed to be having a hard time but made it past Sun down.

About 30 mins before everyone usually goes to roost, she started making this high pitched distress call, 20 seconds apart and kept doing it all the way to roost. She did it for 2 solid hours on the roost so by 9pm I brought her in the house where she will be residing for night. In between calls, she would sometimes make a honking noise with hard out breaths. It was very strange behavior.

I checked everywhere, no predators and she was in her normal spot so it wasn't a territorial call. I'm stumped. It's not gape worm because she's been honking and out breathing for months now. Respiratory? But wouldn't the rest of the flock caught it by now? Is she just a weird bird? I'll try to upload a video I took of her in quarantine tonight. She stopped doing the call but is still honking and out breathing with mouth open. Any clue, anyone?

Gosh, I'm just not sure. From what I've read, gape worm is fairly rare (but it's almost what everyone jumps on when they see a bird's mouth open). So you're probably right that it's not that. She's ONLY gaping when on the roost at night, never during the day???

You can lightly swab the back of her throat with a Qtip to double check - they're supposedly reddish and stringy looking.

When my (now) 5 yr. old group was about 6 months old, I had ONE girl develop some kind of respiratory issue. Maybe they all had it, but she was the only one who showed symptoms, and she was the only one I treated - I did three days of shots (Tylan 50) into her breast muscle - alternating breasts each night. She fully recovered within a week or so, and nobody else ever showed symptoms.

So it's possible that it could be a respiratory thing.

How hot does the coop get in the evenings? If it's an oven, is there a way to run a small fan out there? See if that makes a difference? Or bring her in the house for a night or two and see if she's still doing it...

Another thought...depending on how dusty/dry it is in there, could she be reacting to dust??? Just trying to toss out ideas.

It is pretty normal for chickens to pant with an open beak inside a coop when it is in the 90's outside. Also they usually hold their wings out from their bodies. Occasionally, I will have an oddball hen who will carry on vocally at the top of her lungs in the coop, especially when I am in there. I don't know if that could what she is doing or if she is really in distress. Gapeworm really can't be seen in the throat of a live hen, even though there are old posts on BYC saying that you can. I probably even repeated that after having read it when I was new here. It can only be seen in the trachea or airway when it is cut open after death. Gapeworm and other chicken worms are easily treated with giving SafeGuard Liquid Goat Wormer 1/4 ml per pound orally for 3 days in a row, or 5 days in a row for capillary worm which may also affect breathing.

Thanks everyone for the replies! It took awhile to get back here but I do have a small update. As of yesterday, I noticed a small white wart like scab on one of my other chickens. I brought her in and took to the internet! They have Fowl Pox, well at least this one does. None of the other girls are showing signs but I'm wondering if the gasping and out breaths from my Austrolorp I was originally worried about might be caused by the wet form of Fowl Pox. Fowl Pox presents itself in both dry and wet forms and the wet form can mimic signs of respiratory issues, even though Pox is a virus. Mosquitoes are bad this year as I live next to the Russian River in California. Once this outbreak clears, I'm going against my word and I'm definitely getting them vaccinated. Any insight? Anyone have Pix before?

You are right in the middle of wine country! Wet fowl pox can sometimes be seen in the throat with a flashlight, but it also can affect the nostrils and nasal cavity, trachea (airway,) esophagus (food tube,) and crop. It can cause respiratory problems, but usually they may stop eating because of the pain. That is when they can die either from secondary respiratory infection, or from starving. Eye infection can be a problem with the dry form. Here is some reading with pictures:
https://www.backyardchickens.com/a/avian-pox-how-to-treat-your-chickens-for-avian-pox
http://www.thepoultrysite.com/publications/6/diseases-of-poultry/195/fowl-pox/
http://www.hyline.com/aspx/redbook/redbook.aspx?s=5&p=35
http://animalsciencey.ucdavis.edu/avian/Fowlpox.pdf