Nicole is an ex-Plain Jane, one of Melinda's former friends. She's a talented athlete, and Melinda sees her as a nice person. As with Ivy, it's not clear if Nicole is avoiding Melinda because she's a social outcast, or because she's simply absorbed in her own life. Nicole and Melinda don't jell the way that Melinda and Ivy do, but there's still something there.
What draws Melinda and Nicole together is sports. When Melinda and Nicole play tennis, there seems to be a genuine connection between equals. Nicole also comes to Melinda's closet with the lacrosse team just as Melinda has managed to fight off Andy, who is trying to rape Melinda again.
Nicole is a credible witness against Andy and could be important in making Andy take responsibility for his crimes. She's definitely important in restoring Melinda's good name at Merryweather. We predict a lasting friendship.