She grew up in one of the poorest spots on earth. She couldn't read or write. As a child, she scrounged for food each day for herself, her mother, and her brother. But a chance encounter with a chess coach turned her into a rising international chess star, the subject of a book -- and the protagonist in a future Disney movie. Ugandan teenager Phiona Mutesi is "the ultimate underdog," her biographer says. Those who work with her believe she's 16. But since her birthday is unclear, she might still only be 15, they say. Her father died from AIDS when Mutesi was around 3. "I thought the life I was living, that everyone was living that life," the teenager…