Chick not eating and thin - ideas?

[tk2]

Came home today and my six week chick was not interested in eating her treats and is lethargic. I picked her up to check her out and was shocked at how thin she is under all her feathers. I haven't noticed any bloody stools. She seemed fine yesterday. They have been in their coop area with run for about a week. Her five coop mates are fine.

Any ideas?

 

[tk2]

I did get her to accept a little bit of egg - it seemed like she had a hard time swallowing if that provides any additional insight.