Who is Rachel from Something Blue and what is their importance?

Rachel has been Darcy's best friend since childhood. Not as beautiful as Darcy, Rachel is mature and studious. As a child, Rachel is promoted to the gifted and talented class with Ethan, making Darcy jealous and causing her to make fun of Rachel's class. Rachel attempts to keep Darcy grounded, warning her about becoming an empty woman when the girls are only twelve by using a game called psychiatrist. When Rachel graduates college, she moves to New York City for law school and was followed by Darcy who is looking for the elite social scene. Rachel introduces Darcy to her good friend Dex, who is also a law student.