Who is Aunt Birdie from Tender at the Bone: Growing Up at the Table and what is their importance?

Aunt Birdie is not actually related to Ruth. She is the mother of Father's first wife, Hortense. Birdie, deprived of grandchildren by her own daughter's mental illness, simply shows up at the hospital the day Ruth is born and introduces herself to Ruth's mother, Miriam. Aunt Birdie offers her services as a grandmother, and Ruth's mother is happy for any help she can get. Birdie is just 4'8" tall and over eighty years old, but has a big influence over Ruth's life. For one thing, Birdie employs a cook named Alice, who teaches the young Ruth how to prepare many dishes. Aunt Birdie herself can cook only one dish, a delicious potato salad that is a favorite of Ruth's father.