Amy Szalinski couldn't be more different than her nerdy father and little brother. The quintessential popular girl at school, she loves her lofty status, her hip friends, and cute boys. She's like Regina George or Claire Standish.
Still, if you push aside your stereotypical assumptions of her for a second, you'll realize that she's surprisingly sensitive and cognizant of her family's issues.
Too Hip to Quit
We can see this in her phone conversation at the beginning of the movie. On one hand, she's talking in a quintessentially teenage way about boys and school dances—stuff that might not seem all that "real." On the other hand, she seems to have a nuanced understanding of the strife that is unfolding in her family, something that seems to be lost on her little brother Nick and father Wayne.
Here's her explaining why she can't chill at the mall later that day:
AMY: I've got to hang around a while and keep an eye on Nick. [...] Things'll cool off after today. [...] Mom and Dad had an argument last night and Mom spent the night at Grandma's. I think she just needed a rest. Right—her and me both.
Not only is Amy doing the empathetic thing by putting her family before her social life, but she's also assessing a complex emotional situation in a cool, collected, and—most importantly—mature manner. Much more mature than her old man, at least.
She also becomes the unofficial leader of the group after the kids get shrunk. Sure, Little Russ has his heroic exploits, and Nick uses his brainpower to accurately assess the situation at hand, but Amy is crucial to keeping the group motivated and pushing forward despite constant danger. Notably, we're thinking about her clever idea to use a snack cake to bribe Antie into becoming their steed, without which the group might never have made the trek across the yard.
From Creepy to Canoodling
Of course, we'd be remiss if we didn't mention Amy's burgeoning romance with Little Russ. Although she was a little creeped out by him at first (who wouldn't be after the whole "watching her dance through the window" thing?), she eventually grows fond of him because of his brave and selfless actions towards her and her little brother Nick. This culminates in a kiss, but also in a genuine moment of connection between the two.
Check it out:
LITTLE RUSS: I would have come by, I wanted to, but I just always thought you were too popular to notice me.
AMY: I was too popular to notice.
This is big because it shows Amy admitting the way that she's been superficial in her approach to social life. Amy was pretty mature at the beginning of the film, but she ends the film with the kind of worldiness and introspection that usually shows up in people several decades her senior.
Girl, You'll Be a Woman Soon
None of this is to say that Amy and Russ are destined for lifelong romance of anything of the sort. Instead, this represents the fact that this stressful and dangerous experience has forced Amy to come to grip with a few of her own shortcomings and realize that she has let other's expectations define her in some small way.
It might not be as significant as Little Russ being afraid to tell his dad that he quit the football team, for example, but it's still a big step in her growth as a person.