I'm sorry you are experiencing this with your Pullet. Cockerels and other Pullets can be mean. If you are sure, she did not get get this wound by getting her head stuck and pulling it back out, then you have some Bully within your Flock.
It will be up to you to sit and watch them all interact with her. It could be happening at the feed dish, water dish but, it is obviously happening and its up to you to watch them until you know who is doing what to her. Somebody is guilty. Somebody with beautiful Feathers is the culprit. Of course it could be any Pullet.
Need more answers:
1. First how many chickens do you have.
2. You mentioned you have two Cockerels (one is going) vs Pullets??
3. What is the size of your coop?
4. Are they free ranging or are they in an enclosed run?
5. How is your roost set up?
6. How old are they?
7. What type of chickens do you have?
8. Are they from one flock or have you added more birds at a separate time?
9. Do they stay inside the coop until you let them out side with you?
10. Have any of them laid yet?
Wound Care:
Get your Chicken First Aide kit out. If you do not have one, it would best that you make one.
1. Rinse the wound with normal saline, chlorhexidine, or betadine wash.(Be VERY CAREFUL NOT to get any in her nose, eyes or ears). DO not use H2O2(hydrogen Peroxide)
2. Gently Pat dry the best you can.
3. Liberally apply a Triple antibiotic ointment. (Neosporin is ok) NO LIDOCAINE added (it is toxic to chickens)
4. If you can separate her from the flock into a dog crate in a screened are or house for a couple days, that would be good also. It is important to keep flys off the wound. (they lay maggots)
5. Go to your local Feeder Supply store aka:
Tractor Supply and purchase an antiseptic called Blu-Kote. It sprays Purple and will stain EVERYTHING it touches. But, it will help the wound heal and hide the redness/blood color. Chickens are attracted to the color Red.
6. Keep the Triple Antibiotic Oint on the wound until healed.
7. Feed her scrambled eggs as a supplement with her Chick starter crumbles in it.
8. If you have Sav-A-Chic Electrolytes, Hydro-Hen Electrolytes offer that to her in her water but always have fresh water available too. This will help boost her compromised immune system from the stress of the receiving the wound.
9. Chickens are very tough little birds but rely on us to protect them and heal them up.