One of O'Hara's earliest professional roles was in a US national tour of the musical "Jekyll and Hyde". She next played the role of Young Hattie in the 2001 Broadway revival of "Follies", and then played the role of Young Phyllis. She next appeared in the 2002 Broadway production of "Sweet Smell of Success" as Susan. In 2003 she played Albertine in the Off-Broadway Playwrights Horizons production of the musical "My Life With Albertine", and, in 2004, Lucy Westenra in the Broadway production of "Dracula, the Musical".