Something you could try, is white vinegar diluted 50/50 w/ water and swab it on. My daughter has fought w/ acne since leaving the Army 10+ years ago and after all her efforts, she gets the best result w/ vinegar. It certainly wouldn't cause harm and it might help. DD has done this rather than be on a long antibiotic regimen like for months. Her skin is generally clear now. Have you isolated her at all, I can't remember. It doesn't seem contagious in a normal sense. If she isn't suffering, and it remains dry, I would hold off on culling. If someone else different gets it, then culling is needed, as hard as that can be. She is still a baby so keep notes as to how the seasons affect the "rash". We can be educated that way. That's a good thing about this thread, we learn the odd things that can happen to our birds.