Neck rash in a 5-week-old Welsummer
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Hopefully the No Peck will work. If not you can try some Blu Kote sometimes it will help "hide" the affected area.
Have you let them outside yet or are they still in the brooder.
It looks like she is feathered out fairly well, so if they are still in a brooder you might want to consider space, as being too crowded can also cause unwanted picking/pecking behavior.
If they are outside, place a few perches around so she can avoid the offender(s) and if food aggression is a problem you may want to add another feeder.
Just some thoughts