Head tucked bird

[Compensation]

I have a 9 week old astralorp that was singled out tonight by herself. She is contorting her head under herself shaking her head almost looked like she was pecking her chest. She walked backwards and keeps sitting down, not making any sounds like she is in pain. She wasn't like this 7 hours ago. I seen alot of different answers on here for the same symptoms. How do I know what it is or how to handle it? Thanks for your time.

 

[Compensation]

Also I am feeding country road medicated chick starter grower. They have pine chip and a little bit of straw bedding. Fresh water 3 times a day.

 

[Compensation]

So... to shoot or not to shoot? Still not any better.