First time chicken owner with sick chicky

[Chicken Megan]

I have an Easter egger that is about 15 weeks old. A few weeks ago she was keeping one eye closed and her neck slightly cocked. That has since resolved but now she is lethargic and very thin. She just sort of hunches in a corner. She is eating and drinking and I’ve supplemented vitamins. She is in with 15 other chickens and no one else shows any symptoms.

 

[Eggcessive]

Is she having any trouble walking or balancing? Can you try to get her outside and observe her behavior? Will she eat some bits of scrambled egg and moistened chicken feed? What do her poops look like? Was she vaccinated for anything?