Serama is missing tail feathers

[SJchickens]

My 4 week old serama has always been kind of sickly. Recently we've noticed that she's missing tail feathers. Is there anything we can do to help them grow in? Thank you.

 

[SJchickens]

Also, what could I give her to make her less sickly a bit? She eats and drinks and does whatever chickens are supposed to do, but just isn't very lively.

 

[SJchickens]

Bump. Going to give her nutri drench. Help is still appreciated.