How did Claudia Regan hurt Kelly in a truth game and by her actions and what did it take to diminish Claudia's popularity?

The girls participated in a truth telling game where they would confront each other with their flaws. Claudia told Kelly that she had horse teeth and shouldn't smile so much. Claudia had a sleepover and didn't invite Kelly. Claudia was behind other cruel things that happened to Kelly and to other girls. She was finally disciplined by the principal and her popularity began to decline. Years later Kelly's mother revealed to her daughter how she had suffered through Kelly's sixth grade with her.