Love is a Fixer-Upper

Clary has a younger sister named Arianna. They're the same age, go to the same school, but are completely different. Clary is the popular sister, while Arianna is the one nobody likes, that is until a certain black haired, blue-eyed boy takes an interest in her. When? Where? Why? How? are the questions. Summery sucks, but the story will be much better. Rated T for now, will go up!