For now, don't place her with ANY of the other chicks. She needs her own separate area. The others will peck at her head and either worsen the damage, or kill her. Keep the area as clean as humanely possible, and see if it can heal. Keep her warm, fed, and see if she exhibits any strange behaviors. You can try dabbing on a small amount of Neosporin. It could be her brain, but it might be a less severe case. She'll either pull through, or not. Good luck!