Earthgirl by Jennifer Cowan
Earthgirl follows the eco-evolution of sixteen-year-old Sabine Solomon, who is thrown into the fray one afternoon when she's riding her bike downtown to join her friends, and an idling minivan driver carelessly tosses leftovers from McDonald's out the car window, blindsiding Sabine and leaving her covered in plum sauce. When Sabine tosses the garbage back at the offensive driver, an altercation ensues that is captured on the videophones of her friends. In a technological blink, footage is posted on YouTube, and Sabine finds herself at the center of a heated eco-debate. A crusader is born.