That hair is NOT ballet hair, btw. The face, though, is Pure Bershon. (TM Sarah Brown)
Here is what I remember of this thing which I have not seen in a minimum of 20 years (but in this case is actually 30 years), and did not review or fact-check at all except to find a pic of it on the Internets:
There's this girl, whose name I can't remember. She's in high school, and ballet is her LIFE, and but she also sweats some cute boys (of course) but ain't nobody really got time for that because of ballet. She starts feeling weird, almost passing out, thinking it's just because she starves herself for her art. Her little sister is like, "Damn girl, why do you smell like nail polish? And how come you're so thirsty all the time no matter how much you drink?" And she's all "BUTT OUT, TROLL!" But lo! After some sort of incident at school, we discover it's not merely starvation and overexercise -- turns out, she's A DIABETIC!!! How embarrassing! And tragic. She could DIEEEEEE!!! Of the diabeetus! And her mom and dad go all super-helicoptery and want her to cease dancing IMMEDIATELY (docs say, nah man, exercise is good for the diabeetus, you're overruled, psychos). And she almost passes out in class at one point on account of her blood sugars but remembers she's supposed to eat some LifeSavers candies and drink some OJ and she does and it's ok. And then! There's this audition to join ... maybe a prestigious ballet school? In New York? and her parents are like FUCK THAT, you can't manage this horrible tragic embarrassing disease on your own, you're going to live with us, sedentarily, forever! and she fights with them and is all dramatic about it (teenagers!), but talks them into it eventually. And finally, there's a dance at school and she wants to go and wear jeans (because jeans are cool) and her mom says no way are you wearing jeans to a Formal Dance, and she says GOD MOM IT'S THE EIGHTIES, and they fight, and but then end up compromising on a "plum-colored" pant/sweater combo from a department store and the main boy she's sweating is like damn girl I like your plum-colored pant/sweater combo, let's derail your future with a teen pregnancy (just kidding about that last part, it's very chaste -- the drama in these YA novels you'd get at the Scholastic Book Fair or at like Waldenbooks was all about Ballet- and/or- Clothing-Related Angst).