Who is Robyn Rosselli from Crank and what is their importance?

Robyn is Trent's sister. She is a cheerleader at Reno High School. Kristina suspects, correctly, that Robyn is doing drugs in order to maintain her slim weight and peppy energy. Once Kristina lets Robyn known that she also uses crank, the two become close friends. Robyn shows Kristina how to smoke crank, and also buys crank and resells it to her. Many of Robyn's stories about her life after using crank, such as her rape, parallel those of Kristina. The inclusion of Robyn in this story stresses the idea that drug addiction is something that can happen to any teen, even on who appears to have their life together.