Worried about my 8 week old chick

[Roux6124]

I have an 8 week old chick that I'm worried about. She seems puffed up and slightly lethargic. She wants to roost with the other ladies, and looks like she's thinking about jumping, but doesn't ever jump. She has a little poo stuck to her feathers in the back but her vent is clean. She is exploring the run with the other chicks but sometimes takes laying down breaks. She also feels lighter than I think she should and our 7 week old runt has caught up in size. I will post a picture of her next to the Cuckoo maran that is the same age as her. She the one in the middle, to the right of the Polish.

 

[SmiYa0126]

Hello! I would treat for coccidiosis right away.