TALL AFAR, Iraq -- Buzzing over this northern Iraqi city in her Kiowa scout helicopter, a .50-caliber machine gun and rockets at the ready, Capt. Sarah Piro has proved so skillful in combat missions to support U.S. ground troops that she's earned the nickname "Saint." In recent months of fighting in Tall Afar, Piro, 26, of El Dorado Hills, Calif., has quietly sleuthed out targets, laid down suppressive fire for GIs in battle and chased insurgents through the narrow alleys of this medieval city -- maneuvering all the while to avoid being shot out of the sky. In one incident,...