Videos in Post#4 from Youtube were posted a year ago (on youtube).
If seems like you may have a chronic respiratory illness. Have you not treated them at all?
If your coop has a lot of poop or ammonia odors, this could cause respiratory symptoms. Dusty means just that - is your coop really dusty with no ventilation? Do you cough/sneeze, have burning eyes or runny nose after being inside the coop working/cleaning?
The hen in the video from today has squinty eyes and is sneezing/coughing. I'd clean her eyes with saline, put a dot of Terramycin eye ointment in the eyes and treat her with Tylosin to see if her symptoms get better.
Do check her crop to make sure it's emptying overnight too.
Recent thread:
https://www.backyardchickens.com/threads/open-mouth-breathing-and-squeaking.1669542/
Another of your threads from last year with similar symptoms:
https://www.backyardchickens.com/th...very-frequently-and-shaking-her-head.1611050/