Chicken is laying on her side

[TxFairy]

My chicken is about 7 months old. she is suddenly laying on her side in the yard, without moving. from the looks of it, she hasn't moved much for a while, she is laying in her own poo, even. I moved her into the bathtub, hoping to clean her up, maybe see what's wrong. no signs of injury, except that she will not put any pressure on her left leg, and refuses to even lay on her right side.

This is how she is in the bathtub, now

 

[edits]

New to this but have had the same prob with our silkie. Does it look like she's drunk? Could be Marek's disease (sorry). I've been spoon feeding/drinking him in the bath with a fan (mainly because it's cooler **over 100 F here for over a week** https://www.backyardchickens.com/forum/viewtopic.php?id=265922