Who is Aunt Duffy from One of Those Hideous Books Where the Mother Dies and what is their importance?

Aunt Duffy is Ruby's mother's sister. Aunt Duffy secretly helped Whip be involved in his daughter's life. She also told Ruby who her father was and took her to see his movies every year on Ruby's birthday. Once Ruby arrives in California, Aunt Duffy leaves for a six-month archeological dig with her new boyfriend.