"Translation" was written about reburial of the remains of former inmates of a Magdalene home. The change of narrative voice in the last stanza is related to the identity of the different individuals involved in the Magdalene homes or laundries. Particular nuns carried keys, functioning as prison guards.
Even though the sisters had authority over the "sinful" women, or unwed mothers, their choices were also limited. The sisters and workers changed their names and identities when they entered the convents and work "homes."
When the key keeper relinquishes her post, it seems here that she speaks of the effects of the experience. Like someone infested or possessed with a parasite or a spell she was not her full self. Leaving her job or life itself will bring her the peace that eluded them all when confined in the home.