Chicken limping

[User690263]

I went out to visit my chickens today, and I noticed my 2 year old Golden Laced Wyandotte hen limping.
Additionally, her feathers are fluffed up and she has labored breathing.
Upon examination, I could find no visible injuries, and she didn't react to me moving her legs around. I did not notice any swelling.
She is still interested in food (or at least mealworms) but she definitely does seem to be in pain.
She was completely fine this morning (I let them out around 9 am)
None of my other hens have any issues.
What might this be, and how should I go about treating her?

 

[User690263]

I currently have her set up in a hospital crate, as -since she is already low in the pecking order- I'm worried that the other birds would mess with her since she's clearly not doing well

 

[User690263]

@Wyorp Rock @Eggcessive