Melody Pond (Prequel to The Impossible Astronaut)

This little girl contacted Richard Nixon for assistance, but he did not know who was calling him. She later encountered the Eleventh Doctor and Amy Pond. To prevent a future in which the girl killed the Doctor, Amy fired a gun at her. She dressed in an American astronaut suit. (DW: The Impossible Astronaut) It is possible that Amy attempting to shoot the girl causes the girl to kill the doctor in the future