Zehetner was born in El Paso, Texas, the daughter of Nancy Lynne (née Nelson) and John Carol Zehetner. She attended elementary school in Richardson, Texas, a suburb of Dallas, before moving back to El Paso. When she was 14 she moved to Dallas where she attended the McKinney High School for several years. She also attended the Texas Academy of Mathematics and Science, a post-high school program for students interested in engineering or medicine, for one year.
At the age of 18 Zehetner started an acting career, something she had been interested in since she was 8, and moved to Los Angeles. She appeared in a number of films like Tart (2001), American Pie 2 (2001), R.S.V.P. (2002), May (2002), The Song of Rose (2003) and others as well as in several TV series and commercials. While she is best known for her role as Laynie Hart on the WB's show Everwood, her movies are often from the comedy or the horror genre like May or R.S.V.P..
Recent productions featuring the actress include the film Brick which won the Special Jury Prize for Originality of Vision at the 2005 Sundance Film Festival, in which she plays the role of the rich femme fatale Laura. The soundtrack CD of this film, released on March 21 2006 by Lakeshore Records, features a full unedited performance of "The Sun Whose Rays Are All Ablaze" by Zehetner.
In the thriller-horror film Beneath, she appears in the leading role of Christy.
Zehetner recently guest-starred as Eden McCain on NBC's Heroes for eight episodes. Zap2It.com proclaimed Zehetner as one of "The Underrated of 2006" for her role.
Together with the actors and comedians Tom Arnold and Dax Shepard, Zehetner embarked in 2007 on a USO/Armed Forces Entertainment tour to the Persian Gulf region to meet with service members and sign autographs.
In 2007, Zehetner played together with Marisa Berenson in the short movie Jalouse: Elegante, famous, beautiful, jolie which was produced by the French fashion magazine Jalouse to celebrate their 10th anniversary.