CADY: I know what you're thinking. Home-schooled kids are freaks…or that we're weirdly religious or something…but my family's totally normal, except for the fact that both my parents are research zoologists and we spent the last twelve years in Africa. I had a great life, but then my mom got offered tenure at Northwestern University, so it was goodbye Africa, and hello high school.
Cady starts off the movie self-aware and levelheaded, as seen by the fact that she immediately shoots down the stereotypes that usually accompany kids who are home-schooled. She also establishes that she's had a unique upbringing, and we can be pretty sure that that's going to influence her decisions, interactions, and experiences going forward.
JANIS: Cady, there are two kinds of evil people: people who do evil stuff, and people who see evil stuff being done and don't try to stop it.
Life is full of big decisions like this. What you choose helps shape your identity. Just ask Darth Vader.
JANIS: I love seeing teachers outside of school. It's like seeing a dog walk on its hind legs.
Ignoring the fact that teachers have actual lives outside of the classroom is a practice as old as the teaching profession itself. Because they're so close to their job, it's easy to zero in on that, and only that, slice of their identity.
CADY: You're not stupid, Karen.
KAREN: No. I am, actually. I'm failing almost everything.
CADY: Well, there must be something you're good at.
KAREN: I'm kind of psychic. I have a fifth sense.
Karen's identity revolves around the fact that she's not the sharpest knife in the drawer, so it's kind of shocking, and even a little bit sad, when we learn that she's aware of it, and still doesn't seem to want anything more out of life than to be Plastic. That's also why it's so cool to see her using her "fifth sense" to do the morning weather reports at the end of the film.
CADY: I pretended to be bad at math so that you'd help me, but the thing is, I'm not really bad at math. I'm actually really good at math. You're kind of bad at math. Anyways, now I'm failing. Isn't that funny?
AARON: Wait. You're failing on purpose? That's stupid.
CADY: No, not on purpose. Just, you know, I just wanted a reason to talk to you.
AARON: So why didn't you just talk to me?
CADY: Well, because I couldn't. Because of Regina. Because you were her, her property—
AARON: Her property?
CADY: No. Shut up. Not her property—
Two things here: first, Aaron's exactly right. It's way lame that Cady pretends to be bad at math in order to talk to Aaron. For starters, if he's bad at math, why couldn't she just offer to tutor him, right? Second, Aaron's still right: Cady is acting like a clone of Regina here, right down to telling him to shut up. She thinks acting dumb and mouthing off is the way to attract Aaron, and she's super-duper wrong.
CADY: You know I couldn't invite you. I had to pretend to be Plastic.
JANIS: Hey, buddy, you're not pretending anymore. You're plastic. Cold, shiny, hard Plastic.
Janis and Cady's fight in the street is a wake-up call for Cady. She has turned to Plastic. She dresses like them. She talks like them. She's self-centered like them. She's not doing Plastics sabotage anymore; she's just hanging out with her fellow Plastics—and leaving Janis and Damian in the dust.
JANIS: See, that is the thing with you Plastics. You think that everybody is in love with you, when actually, everybody hates you. Like Aaron Samuels, for example. He broke up with Regina and guess what: He still doesn't want you. So why are you still messing with Regina, Cady? I'll tell you why. Because you are a mean girl! You're a b****!
Preach, Janis! Cady's in denial that she's a Plastic because, underneath that haze of hairspray and lip gloss, the kindhearted, levelheaded girl that we met at the beginning of the movie is still in there, and she knows that the Plastics are awful.
CADY'S MOM: This is the fertility vase of the Ndebele tribe. Does that mean anything to you?
CADY'S MOM: Who are you??
After half the school thinks Cady threw Regina in front of a bus, we're pretty sure Cady's asking herself that, too.
CADY'S DAD: Maybe you should come back and be home-schooled again for a while.
CADY: No, the only thing worse than going back would be not going back.
CADY'S DAD: How bad's it gonna be tomorrow?
CADY: Remember when we saw those lions fighting over the wart hog carcass? I'll be the wart hog.
CADY'S DAD: You're not a wart hog. You're a lion.
Dad's right. She's a lion, and the fact that she realizes she has to suck it up and show her face at North Shore is the first step toward Plastics rehabilitation.
NORBURY: Well, you didn't write that whole book yourself. Did you tell Mr. Duvall who else did it?
CADY: No, because I'm trying this new thing where I don't talk about people behind their backs.
AARON: That's all right. Getting hit by a bus is pretty good punishment.
AARON: Welcome back, nerd.
That's our girl. Aceing her calculus quiz and not being a gossip. When Aaron welcomes Cady back, he isn't just welcoming her back to total math class domination. Grool.
CADY: I had gone from home-schooled jungle freak to shiny Plastic to most hated person in the world to actual human being. All the drama from last year just wasn't important anymore. School used to be like a shark tank, but now I could just float. Finally, Girl World was at peace.
By the end of the film, Cady's settled into a comfortable identity: she's just herself. Her "new student" sheen has worn off and the implosion of the Plastics also destroyed North Shore's network of cliques. She's embraced the worldview of international spiritual leader Mary J. Blige: "No more drama, no more drama."