I assume you are speaking of the death of Cherry's boyfriend, Bob.
Cherry Valance is a cheerleader who drives a Corvette and dates Bob Holden, one of the most popular of the Socs in Susan E. Hinton's novel, The Outsiders. According to Cherry, Bob "could be sweet sometimes," but when he gets drunk, he becomes dangerous. After beating Johnny Cade severely some months before, Bob and his friends come upon Johnny and Ponyboy in the park shortly after they had been seen with Cherry after the drive-in movie. When Bob and his Soc pals try to drown Ponyboy, Johnny responds by killing Bob with his knife.
When Dallas Winston meets up with Johnny and Pony at the old church, he tells them about a visit from Cherry.
"She said she felt the whole mess was her fault... and would testify that the Socs were drunk and looking for a fight and you fought back in self-defense.
On the night of the rumble, Cherry visits with Ponyboy and Two-Bit to let them know that the Socs will not bring weapons to the fight. She and Ponyboy speak once again, and she tells him about her times with Bob. When Pony asks her to visit Johnny in the hospital, she refuses.
"He killed Bob. Oh, maybe Bob asked for it. I know he did. But I couldn't ever look at the person who killed him. You only knew his bad side... I know I'm too young to be in love and all that, but Bob was something special."
Cherry feels true remorse about her part in Bob's death and the eventual injuries received by Johnny. It affects her so strongly that she tries to make amends by agreeing to testify against her boyfriend and by providing the greasers with inside information about the rumble. She admits that she has problems of her own, just like other people.