Who is Jill (Jillie) from The Deep End of the Ocean and what is their importance?

Jill (Jillie) is a teenager and Pat Cappadora's cousin. She helps Beth out with the children, and acts as a sort of nanny to them. Jill is with the kids when Ben disappears at the hotel. She later spends afternoons with the family and provides a great deal of comfort and care for Vincent, who is virtually ignored by his mother.