Who is Hannah from A Dog's Purpose and what is their importance?

Hannah is a girl who lives down the road from Ethan's grandparents who live in the country on the Farm. She brings brownies one day and she and Ethan fall in love. Bailey observes that they wrestle together. Hannah appears again in the dog's last reincarnation. She is now an old woman and Bailey, now a black labrador, named Buddy reunites her with Ethan.