Sick chick? (2 weeks)

[Megaletta]

We have three two-week old chicks (all different breeds). The salmon faverolle has been hiding under the heat plate more for the last two days. She’s still eating and drinking at least some, but is far less active than the others. Today I took them outside for a bit and between that and afterwards, also have noticed that she sitting a lot. Even in the grass she would sit down to peck. I don’t see any obvious leg injuries. She seems ok when she does walk.
Would appreciate any thoughts or suggestions in terms of what to check or do!

thanks,
Megan

 

[cherrynberry]

Any pictures?

 

[cherrynberry]

I used to have a chick who would never go toward others and just stay next to the heat source all the time. But that chick has now grown into a pretty hen! So it may not be too big of a problem.