Sprains can very common in chickens from injuries. I would limit her activity, if she isn’t already limiting it herself, and keep her in a dog crate or pen, or in the coop where she cannot jump to roost or get mated by a rooster. Metacam is a good anti-inflammatory drug and helps with pain, so hopefully, she will recover. But it can take several weeks to heal. Here is a diagram of the skeleton where you could pinpoint the area that is hurting. Is it the joint between the metatarsus and the tibia/fibula that is swollen?
Ouch poor girl! You have some great people helping you here! 
for your girl!
