Link to other thread about this chicken.
https://www.backyardchickens.com/threads/sick-hen.1568168/ It's far more helpful if you keep posting to the same thread instead of starting new ones on the same exact subject.
Thanks for reposting the video. I'm sorry, though, it doesn't tell us much.
Breathing fast and hard can be from stress, and stress can be caused by a lot of things. Weather extremes. Trouble laying an egg. Bullying by others. Infection. Clogged nares.
We need to see a photo of her most recent poop.
Is she able to stand without wobbling? Is she able to walk normally? Is there a bad odor to her poop? Is there a steady drip of yellow mucous from her vent?
Have you looked at the skin around the vent for lice?
Have you checked to see if her nares are clogged? Clogged nares can cause labored breathing.