Wish Upon a Star - Blair Treu

Handsome, considerate high-school jock Kyle Harding is the only taste the Wheaton sisters share. Tall, fashionable, popular airhead big sister is dating him, but fails to truly appreciate the young gentleman, let alone contemplate a serious relationship. Nerdy kid sister Haley hates the waste and expresses her envy by thoughtlessly wishing at a 'shooting star' (comet) to be Alexia. To their stupor, that happens the next morning. Forced to live each-other's lives, but unable to do it well by the other's standards, the sisters soon hate each-other even more and deliberately screw up. Gradually, they realize they would only both lose out, learn to appreciate the other's values and reconsider their own. Remain the matters of obviously utterly confused Kyle, and new neighbor boy Simon, whose no longer secret crush on Haley was confounded by Alexia.