Despite being the very first character we meet in the movie, Jane Burnham is in more of a supporting role—both in the movie overall and in her family. And of course, she knows it. When we first meet her, we can tell she is (like a lot of teenaged girls) buckling under the weight of her insecurities.
For example, on the morning we first meet the Burnhams, Jane is spending her pre-school time researching boob jobs—so it seems she's not super happy with her figure. To make matters worse, her mother comments on how "unattractive" her outfit is. With a family like this, who needs enemies?
Speaking of (crummy) friends, she's close with a girl named Angela who's always talking about how gorgeous other people find her and how many men she's been sleeping with… and you can tell by Jane's awkward and terse reactions that all this chitter-chatter doesn't do much for her own self-esteem.
Beyond the standard teen angst, Jane has extra trouble at home. Sure, some of that is normal teen stuff, too—her parents seem to be soul-drained aliens, but who on earth can't relate to that feeling?
On top of that, though, her father's mid-life crisis definitely widens the distance between them, since she doesn't particularly appreciate when Lester starts perving on her friend Angela:
JANE: I'm serious, though. How could he not be damaging me? I need a father who's a role model, not some horny geek boy who's going to spray his shorts whenever I bring a girlfriend home from school.
At least Jane knows that her dad is being irresponsible, right?
Janie's Happy(ish) Ending
Things take a turn for Jane when she meets Ricky, who is exactly the opposite of her. He's super confident and self-assured, taking criticism in stride, and he thinks that Jane is awesome (and tells her so).
So, between modeling good self-esteem and complimenting Janie up and down, Ricky seems to help Janie become a stronger, more self-assured girl—to the point where she can call Angela on her braggy oversharing about her sex life and defend Ricky and herself when Angela is being rude or demeaning.
She never really gets resolution with Lester, unfortunately, but Lester at least dies knowing that Jane (according to Angela's reporting) is doing really well and thinks she's in love. So, we suppose that's a fairly happy ending for her storyline.