It could be a cyst or tumor. Those can be common in chickens all over, but common around the neck. Is there any scab or mark on the skin under the feathers.
The diet is terrible, and not balanced. Is she eating and drinking? Layer or all flock/flock raiser feed should be what she is getting. Can you get a picture of the inside of her beak, in case she has any canker? Is there any yellow material inside her beak or on her tongue? Is her crop...