There is a vet approved three day treatment that entails dipping the legs in gasoline and letting them dry then rubbing in a layer of A&D Ointment.
Apply A&D Ointment only on the second day.
Gasoline dip/dry and A&D Ointment on the third day and the treatment is over.
It doesn't matter if dirt...
Those legs look like she has Scaly Leg Mites. I would smear a thick coat of Vaseline on her legs pushing it up under the scales. Repeat every two days and do it for a month or more.
Carefully check the legs on the rest of the flock for any sign of lifted scales and treat any others that have it.