Amelia's basically Jin's goal for the novel. She drives him—unknowingly—to try and be someone he's not. How does she do this? She's just a nice, white girl after all, and even though she's popular and hangs out with popular Greg, she's not mean.
We know this because she's not just willing to hang out with Wei-Chen after school, she's also truly gracious to him. She tells Wei-Chen:
"I'm really glad you're here with me, Wei-Chen. There's just no way I could do this by myself. Something about little, pink, furless mice… Eech. I wouldn't be able to deal." (5.61)
See what we mean? Amelia's cool. Plus she genuinely seems to like Jin. She reveals to Wei-Chen, for example, that she "'actually had a lot of fun'" (8.43) on her date with Jin.
However Amelia's also maybe a little naive, a little wishy-washy. When Jin walks up to her after their date but then ignores her, she just stands there looking confused, with a thought bubble of ellipses (8.84). We don't blame her—Jin is kind of confusing.
But she doesn't say anything to defend Jin when Greg says, after Jin leaves, "'See what I mean? He's a nice guy, but he's kind of a geek. I mean, what's with the hair?'" (8.92). That's the last we see of her because it's clear that, as nice as she is, she's not strong enough a character to have Jin's back.