Separate her, let it heal, watch her neck overtime as it heals. Was it one chicken pecking her? Maybe remove that chicken and when she is healed let her back in. Watch closely and if anything happens separate her again. I dont know much about what to do.
Keep her separated for sure and make sure she's eating and drinking. It's going to have to be cleaned. I clean my chicken wounds with iodine mixture. I also have vetericyn spray that is picked up at the feed store. It needs to get cleaned. Once it's cleaned you want to use some triple anti biotic ointment on it. Don't use any with pain relief, just the regular stuff. Then let the healing begin. Make sure it stay clean!!! Otherwise it will get infected and she might need antibiotics to help. Don't cover it, it needs air to heal. She needs to stay away from other chickens until it fully healed. I mean feathers are grown back. The other chickens can pick at the new feathers, so keep that in mind.