Chanel #4 was part of the Kappa Kappa Tau sorority and Chanel Oberlin's clique The Chanels, until her death that is mentioned in Pilot.
Pilot
It is mentioned by Chanel Oberlin that Chanel #4 got meningitis and, despite Chanel #1's objections, left to go home, where she eventually died. She was one of The Chanels and part of the Kappa Kappa Tau sorority.
Chainsaw
Chanel Oberlin refers to Chanel #2 and Chanel #4 when she says that she turned Hester Ulrich into Chanel #6 after two Chanels died because she is running out of minions.