Who is Joy from Lamb: The Gospel According to Biff and what is their importance?

Joy is the only concubine among eight who survives when Biff releases Balthesar's human-eating demon. The other seven become breakfast. Joy inherits the Magus' fortune and lives in Kabul. When Biff and Joshua pass through on their way to Israel, Joy welcomes them into her home and entertains. Biff benefits the most from her hospitality.