My silkie chicken is lethargic and stopped eating

[silkiemama01]

My 15 weeks silkie chicken has been lethargic for a couple days. She was still eating and drinking yesterday but has stopped today. She is standing still puffed up and occasionally chirps loudly and pants a little. I don't know what has caused this but the other chickens in in the flock are fine.
What do I do to get her better?

 

[PippinTheChicken]

What are you feeding?

 

[silkiemama01]

What are you feeding?

A crushed grower mix. It's plenty fine enough for her to digest properly so I don't think it's a crop issue.

 

[charlotte-and-the-bees]

How’s she doing?