This reminds me of something that one of my Dutch bantam chicks had a few years ago. The chick was (if I remember right) about 4 weeks old when she suddenly started developed black scabby skin really similar to what your hen is showing. She lost all of the feathers in the area.The scabbiness got worse and worse, then gradually got better. I don't remember if I applied anything to the area; if anything, I probably used neosporin. Eventually, all of the scabbiness and blackness disappeared and the feathers grew back in. However, the chick died randomly when she was about 12 weeks old, so maybe there was an underlying problem for which the neck scabbiness was a symptom.
For your hen, I would keep spraying her with your infection spray and/or applying antibiotic ointment at least once a day. Other than that, just watch for further symptoms.