Sue Snell is an intelligent, popular girl. She had been dating Tommy Ross for six months. And she had had a sexual relstionship with him for two months. She bullied Carrie, but far less than Chris Hargensen and her other friends. She also participated in the shower incident. There however, finding out that she didn´t know about a period feels very guilty about her behaviour and also feels disgusted about Chris´s behaviour after that regarding the incident. She therefore breaks with Chris and propeses to Tommy to take Carrie to the prom instead of her ina way to make it right. Although he was against it first, he mellowed to it later. She also wanted him to do it, because she was worried, that Tommy may have gotten her pregnant and didn´t want to raise the issue yet.
While the Prom was happening, Sue decided to stay at home, yet she had a feeling something was going to happen. Several hours later, the town began to whistle and Sue had to look from the window. She saw Ewen High School on fire. She rushed to her mother´s car and drove to the scene. When she arrived the school exploded and had therefore an accident with the car. When she exited it, she saw a nearby gas station explode. She then went to the town sherriff nearby and tried to tell him about what was happening, something she knew necause of the telepathic broadcast of Carrie, but he interrogated her instead of listening to her, which forces her to look for her alone. Sue knew, that Carrie did all of this in revenge for the prank pulled on her and Tommy and that the prank also killed Tommy on the way.
A while later she finds the dying Carrie in a lot with a burning car. She was able to find her, because of her "telepathc broadcast" and invited the girl to enter into her mind to prove her, that she wasn´t involved in the prank and that she never really hated Carrie. Carrie expored her mind and realises she is speaking the truth. Carrie dies but not before transmitting to her everything about her life to her forcing her on the way to see for herself how ugly she has been to her before this. She also experiences, for a short time, what happens in the mind of someone, when that person dies. After that she finally has her period again. She suspects it was Carrie´s doing, but doesn´t know, if that was an act of retribution or an act of gratitude. She later identifies Carrie´s body, when the authorities come to take it.
After these events the White Commission tried to make her a scapegoat for what has happened, but fails to do so. Years later she wrote the book "My name is Sue Snell" to tell the events from her perspective, where she defends Tommy´s and her actions and where she warns, that something like this might happen again. It is impled, that all the events surrounding the Black Prom have broken Sue´s heart to the core. She only longes for peace and has begun embracing death driven by the experience she had, when she witnessed Carrie die in such a close manner. For her it is as though she is condemned to follow her after her death because of it.