Born in Scottsdale, Arizona, Hanratty is the youngest in a family of five girls and three boys. In 1997, she moved to Los Angeles.
Hanratty has appeared in several films and television series including the 2006 ABC Family original film Hello Sister, Goodbye Life, opposite Lacey Chabert. In 2006, she was a recurring character through seasons two and three of The Suite Life of Zack & Cody as Holly, a little girl whose father is a con man and once stayed at the Tipton. That same year, she appeared in the ABC film Stephen King's Desperation, and had an uncredited minor role in Pirates of the Caribbean: Dead Man's Chest. From 2006 to 2009, Hanratty had a recurring role on the action-drama series The Unit with her older sister Danielle. In 2006, she appeared in the film The Santa Clause 3: The Escape Clause, playing an elf named Glenda. She also played Chrissa in the 2009 film An American Girl: Chrissa Stands Strong.