Not sure what it is but zinc oxide and tea tree oil work wonders healing various skin conditions. Have used them both on our horses with great success. However, you probably want to call the vet out just in case it's a sign of something more serious.
I also thought ringworm. Until the vet gets there, you might want to try Banixx on her twice a day. My mare has an off-and-on fungal infection in her ear, and Banixx is the only product that gets rid of it.
Im also considering ringworm, hard to tell from the pictures lighting. Usually you can’t go wrong with zinc and a natural healing aid and antifungal like tea tree oil or coconut oil, that’s what I do with my dog.