Buff Orp hen limping

[tigmata]

Yesterday I noticed one of my hens (she is about 7 months old) is limping/hopping and not really using her left leg to walk. Her tail is down and she just sits unless I walk over to her and then she'll do the limp/hop shuffle to move away. Easy to catch as I can walk faster than she can shuffle.

Her left foot looks fine, and I squeezed up that leg and got no response from the hen that I was hurting her.

Any ideas? Poor thing looks like a bronze rock in the chicken yard. All the other hens are politely ignoring her.
Thanks!