The tagline for American Beauty is "Look closer," and that's exactly what you need to do with Angela Hayes.
At first, she seems like an almost stereotypical sex kitten. She wears tons of makeup, revels in male attention, and just generally tries to play up her sex appeal—in large part because she's decided she wants to be a model.
In fact, she claims that whenever she went out to dinner with her parents as a (younger) kid, the adult guys at the Red Lobster would just stare at her—and given that she becomes Lester's superfantasy, we don't really find that so far-fetched. Teen boys love her too, apparently. She tells Jane that they think about her when they masturbate:
ANGELA: No, I liked it. And I still like it. If people I don't even know look at me and want to f*** me, it means I really have a shot at being a model. Which is great, because there's nothing worse in life than being ordinary.
So, if you're not looking at Angela too critically, you'd think that she was actually super confident and even arrogant to the point of being unbearable. However, at the end of the movie, we see a totally different side of her. After a whole movie of her pretending to be this experienced sexmonster, she ends up admitting to Lester that she's a virgin.
Like a Virgin
After that, it's like a veil drops and reveals the true Angela, who is vulnerable and (it seems) really, really insecure. Turns out, all that bluster was just a front, and when she reveals her actual inexperience in that arena, she's super embarrassed:
ANGELA: I still want to do it. I just thought I should tell you, in case you wondered why I wasn't… better.
Once she recovers from all that, we get a glimpse of a down-to-earth, friendly girl who is able to have a sensitive, empathetic conversation with Lester. We like this Angela, so it's too bad the movie ends right after we meet her.