In 1996, Barnhart began her puppeteer career performing on "Once Upon a Tree" performing Mara the Beaver and Mrs. Peeper the Owl. Barnhart made her Broadway debut in 2003 and is a featured performer in the Tony Award-winning musical "Avenue Q", in which she also appeared Off-Broadway. She was a regular puppeteer on the Nickelodeon series "Oobi", playing Mrs. Johnson and various incidental characters. She also stars as Cleo on PBS's literacy education series, "Between the Lions", and performed the puppetry for Kanga and Owl on Disney Channel's "The Book of Pooh". Barnhart is a "Sesame Street" Muppet performer who took over the roles of Mama Bear in 2001 and Gladys the Cow in 2002.