Hen won't sit on roost; appears slightly lethargic; HELP

[R_V]

So recently one of my hens (Popcorn) has begun to remove herself from the flock. The day I noticed her not being as active as before was sometime late Friday afternoon. I chalked it up to nothing serious so I let her be but considering she hasn't reverted to her normal energy and is now unable to roost, I'm wondering if this is an issue and if it is cause for concern. I did a revision on the leg she's not able to put as much weight on and there doesn't seem to be any signs of bumblefoot (she's been treated for it once before). Attached are pictures. I also reviewed her behind (considering another of my ladies is currently being treated for wounds around her vent) and there doesn't appear to be anything there other than trailings of poop. Normally she runs when called for a treat but lately she either ignores my voice completely or walks slowly towards me. Otherwise, she is eating and drinking perfectly fine. She does not reject the treats. Popcorn will be four years old in October. Any remedies that I can undertake, please let me know. Even if the cause is not immediately evident, if her case looks similar to something else out there, please advise.

Also, should I separate her from the flock or let her sleep on the bottom of her coop?

 

[chickenlittle21]

Is she laying?

 

[R_V]

Is she laying?

I don't believe so. She has been finding a different nook to snuggle up in. Possibly to lay?

 

[chickenlittle21]

Maybe she has an infection