I've tried the separation partition
@coach723 mentioned, and my injured chick was so frantic to be with the others, she wouldn't quit trying to make a jail break. I was concerned about her level of stress affecting her recovery.
It just broke my heart to see the pile of chicks squeezed up against the partition screen on one side and the injured chick trying to smoosh into the pile from her side. After a couple nights of this, the chick did finally manage to squeeze herself into the other side with the other chicks. I left her there, and none of the chicks bothered her head wound. (A rooster had scalped her when they were all outside for a day trip.) But I watched the group closely for signs of pecking the wound, not trusting them completely.