That's a bad case of scaly leg mites. They can literally eat tissue all the way through a leg.
Apply Nu-Stock to her legs/feet as well as applying it to roosts inside the coop. The mites can go from one bird to another while roosting, a thin coat of Nu-Stock on the roosts will prevent that from happening.
Wear disposable gloves when applying the Nu-Stock. It can be found in the Equine section at a feed store.