Sick chicken jerking her head backwards while pushing her body against the wall

[JuliaSunshine]

One of 31 week old Light Sussex pullets looks sick since this morning, 7 hours ago. She doesn't move, eat or drink. I tried to feed her water but she couldn't swallow it.
She drooled for awhile and then keeps jerking her head backwards while pushing her body against the wall. There's some poo dried out hanging under her vent but the vent itself looked clean even though it kept pulsing. What could it be? I couldn't feel her crop which means it's empty? She free range with no fence all day.

 

[JuliaSunshine]

 

[Vicky Ann Painting]

Do your chickens get enough grit? Is there possibly a crop impaction? http://www.poultrydvm.com/condition/impacted-crop

 

[Vicky Ann Painting]

Or maybe a problem with the vent? https://www.thehappychickencoop.com/chicken-vent-disorders-and-pasty-butt-treatment/ @janiedoe Can you help?

 

[Tookie]

How old is she? Could you get a video of her behavior? Any lice or mites?

 

[Vicky Ann Painting]

Egg binding?

 

[JuliaSunshine]

Do your chickens get enough grit? Is there possibly a crop impaction? http://www.poultrydvm.com/condition/impacted-crop

My chickens free range so they pick up grit as they please. I couldn't feel her crop being hard. Thank you.

 

[JuliaSunshine]

How old is she? Could you get a video of her behavior? Any lice or mites?

She's 31 weeks old. Can't see any lice or mites. I'm uploading a video now. Thank you.

 

[JuliaSunshine]

I shared a video on the original posting. Thank you.

How old is she? Could you get a video of her behavior? Any lice or mi

 

[Eggcessive]

She looks to be having a neurological problem causing the twitching. It could be seizure activity or something affecting her brain. A head injury, vitamin E deficiency, or disease could be possibilities. Does this activity stop? Could you start giving her some human vitamin E softgels 1 daily into her beak, along with 1/4 tablet of B complex or other chicken vitamin? Is she drinking or eating? Oh I see that she is not. Try holding a cup up to her beak and dipping her beak for a second.