Who is Mlle. Albertine Simonet from Remembrance of Things Past and what is their importance?

Mlle. Albertine Simonet is a girl at Balbec. She is a part of a group of girls that the narrator admires. Albertine's father is a rich merchant. She and the narrator become friends, and he soon falls in love with her. Albertine later visits him in Paris the next year.