Rittenhouse was born in Los Angeles and grew up in Pasadena. One of her first roles was in lower school, when she was cast as the Balloon Girl in her all-girls academy's production of the musical Gypsy. She continued performing in high school, but never thought of it as a career. Rittenhouse attended the University of Pennsylvania, where she studied Romance languages. Afterwards, she decided to study acting at the Atlantic Theater Company in New York City.