You have the stepmother and the stepsisters, I never really understood why the movie needed to include another villain. It kinda tones down the other three, especially the stepsisters.
shareI think they needed to be too dumb to humiliate Sam on their own.
shareShelby is more than a villain. She's a strong competitor.
shareI think it was needed to show how pathetic the stepsisters really were. With Shelby as a character they weren't just seen as jealous evil girls who lived for nothing but to ruin their stepsister's live but also to be seen as wannabe popular girls who even gave her a Prada (fake!) bag just to try to be friends with her, and in the high school world there is nothing more pathetic then a wannabe.
"Who lives, who dies, who tells your story"