Sophie should tell the person who she trust about that problem.
Sophie should find in her class a person who is also shy like her and won't treat her bad like other girls in her class do.
Sophie should tell Helen about her problem, so they will find a clue how to stop the mean girls from being unkind to her.
Sophie shouldn't feel worry about the teacher who dosen't notice what's happening in her class - Sophie can tell the psychologist about her problem.