Gurgling/sneezing? Please help!

hi everyone!
I started with chickens this spring. They are now 20 weeks old.
One of my GLW pullets started making a strange gurgling congested sound, accompanied by a head shake, almost like a sneeze or cough (I've never seen a chicken do either, so not sure!). It's been about 10 days now. It took me awhile to figure out which chicken was making the sound because she otherwise is looking and acting totally normal, and the sound happens infrequently. Once I found out who it was, I removed her from the flock; she is now on a dog crate on the deck. Occasionally when I pick her up I can hear rattling in her throat, and also noticed it one evening while she was sleeping.
I have been treating her with essential oils, garlic, and herbs for two days now.
It has been a very smoky summer due to nearby wildfires. This gurgling began right after a run of the worst days we've had all summer. I wondered if maybe she has some ongoing irritation from all the smoke? She may have been more susceptible to it, as she was stressed by a narrow escape from a dog that entered our yard about a month ago - he actually snatched at her twice, although she was lucky and got away with nothing more than a bald patch on her back.
So to sum up:
- a strange gurgling sound with a head shake several times throughout the day, began about 10 days ago
- occasional rattling noise in her throat
- otherwise completely normal!
- not really improving, but also not getting any worse
I took a video so that you can see what I'm talking about. I will upload that separately.
I would love to know what I might be dealing with, and what I should be doing about it. Thanks so much for your help!

 

Okay - I've never uploaded a video to youtube, so hopefully this works! Here's the link:

 

Well, that's reassuring! I was thinking that if this was something really worrisome, surely she would be looking sicker by now! But, being a newbie, I wanted to be cautious.
They are on Natural Harvest Non-GMO 18% crumbles. I'm just about done that bag, and then I think it'll be time to switch to the next step, I think it's 15% - my olive egger has been laying for three weeks now, and I think the others must be close. Other than that, they get some fruit and veggie scraps, a handful of bird seed (mostly BOSS) to bring them in from free ranging (they free range for a few hours every few days, whenever I can be out in the yard keeping an eye on them), and the occasional treat of meal worms.

 

No secretions at all, from nose, mouth, or eyes. Just the gurgling sound and head shake. I live in Canada, and Tylan is banned here. I'd prefer to stay away from antibiotics, anyway, unless I'm absolutely sure it's warranted.

 

Oh, and they have a nipple waterer, so that's nice and clean.