Dermatological issue?

[Japetus]

My gooses neck is for quite some time now -months- in this condition. Would anyone know if it something that can be treated? Has not spread elsewhere in her body nor in to any other bird in the coop.

 

[Eggcessive]

Have you checked for mites or lice? Could another bird be “overgrooming” her? Or could she be rubbing her neck on something to scratch an itch?

 

[Japetus]

She's the only goose among chickens so no other bird dares to groom her -she does so though all the time to other chicken-. No visible signs of lice on her or any other birds in the coop, it's high time though I treat all the birds and the coop again..
Her upper neck is the only part of her body that can't be groomed by her beak...