She will need a vet for that, I'm afraid. Have you ever noticed her leg being at an odd angle, or a limp earlier in her life? Is her hock or elbow joint swollen as in some of the links I gave earlier?
I don't know a lot about leg bone deformities in chickens, but there are many different kinds of deformities that can progress in age, and many involve the hock tendon which will rupture. Some of these are called valgus-varus deformities, and in the past have been called twisted leg or perosis...