Caroline Eastwick was a woman chosen to be buried alive in order to conceal the artifact.
Episode 3 - Buried Alive
After creating the proper pattern, the group attempts to contact her via seance in order to find the second artifact. It works, and she speaks to them through Sarah. It is not until they unearth her coffin that she reveals that they must bury an unwilling soul, one of them, in her coffin in order for the artifact to be unearthed and her spirit to be set free, reason being she knew if she had told them in the beginning, the group would not have gone that far. It is Justine who is chosen to be buried alive in her coffin, as much of the group mistakenly believes she's in league with the evil of the house.