Out of the Womb — Kim Antieau

Carey lives on the generation spaceship Mercury with her parents and thousands of other space travelers. Her parents are Colonists who believe they have a right to leave the ship and colonize a habitable planet. The Counselors, who make the laws and govern the ship, refuse to let anyone go. Negotiations break down between the two sides and soon violence erupts, and Carey's life is changed forever. (This short story was originally published in Isaac Asimov's Science Fiction Magazine.)