Jerkass Woobie: Christy becomes a Jerkass when Dark Heart makes her good at sports, but beforehand the poor girl didn't think she was good at anything. This is why she ends up assisting Dark Heart in his plan, 'cause if she doesn't she'll go back to how she used to be.
Padding: It had a musical number at the end that was pretty much just there to make sure it fulfilled the bare minimum for screentime. The song itself was over six minutes long and over half of it consisted of endlessly-repeated chorus (ostensibly to cover the end credits).
Also, keep in mind that Christy's peers kept looking down on her and making fun of her for not being good at sports. It was as much the result of not being good at sports that drove Christy over the edge, not the mere fact that she wasn't good at sports.
Of course, this also led to her agreeing to kidnap others so that she wouldn't lose her prowess at sports, which places it pretty firmly in this category.