Who is Maggie (Mary Magdalene) from Lamb: The Gospel According to Biff and what is their importance?

Maggie becomes a friend of Joshua and Biff when they are all quite young. She loves both, but Joshua especially. However, she can never have him for a lover or husband, because God does not allow it. Maggie must marry Jakan, a childhood bully who becomes a wealthy Pharisee, due to a family arrangement. She does not see Joshua or Biff for the better part of two decades while they travel and Joshua learns to be the Messiah.