Rizzo deserved to be the real hero of 1950s-set cult classic adaptation of the Broadway show of the same name, hers is a far more progressive story than Sandy's and fits more succinctly with Grease's overall message of self-discovery and expression.
In Grease, Rizzo is painted as one of the villains, seemingly bullying Sandy when she turns up at Rydell High - partly because of her resentment at Sandy's moral purity and how easily she is accepted by the school's social hierarchy. Her arc is easily the movie's most interesting as the emotionally guarded but judgmental leader of the Pink Ladies faces up to the reality of teenage pregnancy and the question of dangerous reputations. She has a tough exterior, but she has a heart of gold, but she's largely just one of the most prominent ing characters alongside the likes of Frenchy.
Rizzo may be mean to Sandy (chiefly when she sings "Look At Me, I'm Sandra Dee") but that song is largely misunderstood in of what Grease was actually about and in reality, Rizzo's forthright sexuality and unwavering commitment to her identity, no matter what the perception, makes her a far greater character than Grease's billed "heroes" Sandy and Danny.
"Look At Me, I'm Sandra Dee" is actually a song about conflict but it isn't just a matter of Rizzo being mean to Sandy because she's different or refuses to smoke, drink or be promiscuous. In Grease's world, Sandy is from a higher class that is obsessed with being "proper" and who are defined, more than anything, by a shallow commitment to appearances - which is why Danny's is shown to throw away his own identity to take up sports and become what Sandy's family might consider "acceptable". It may be cruel to Sandy, but the musical pulls no punches in suggesting that Rizzo's mockery of Sandy's reductive background is deserved and Sandy's transformation at the end of Grease is in fact an act of liberation.
Despite that logic, Rizzo is the character most held back by her "reputation". As she sings in "There Are Worse Things I Could Do", she faces persecution for being promiscuous with boys and for dressing provocatively. In the stage version, she's mocked for having large breasts. She is very much a victim of gender and sex-shaming and it barely even makes sense in the logic of the story's celebration of free expression and liberal spirits let alone watching it back today. Rizzo owns her sexuality and she is one of the only main characters who doesn't go through a real identity crisis, sticking to who she is even as she's forced to weigh up her future because of her pregnancy scare.
Ultimately, Rizzo is also exactly who Sandy aspires to be by the end of Grease, in the film's greatest irony. She might be castigated for the exact same behavior that the T-Birds are lauded for, but she is, in fact, a trailblazer, not only for Grease's audience and the modern adoption of sexual liberty but also for Sandy specifically. The black outfit, the smoking, the expressive attitude, the swagger... All of it belongs not just to Sandy's idea of the opposite of what her prim and proper background has shaped her to be, but to Rizzo as the model. It's only when the film - through Sandy's eyes - casts off the idea that Rizzo is somehow deserving of victimization (by literally adopting her identity) that everyone comes to a happy ending and viewers of Grease absolutely need to pay her due respect.
