Zehetner was born in El Paso, Texas to John Carol Zehetner and Nancy Lynne Nelson. 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 was 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 with the actress include the film Brick (directed and written by Rian Johnson), which won the Special Jury Prize for Originality of Vision at the 2005 Sundance Film Festival, and 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 her. In the thriller-horror film Beneath, the first co-production of Paramount Classics and MTV Films (directed by Dagen Merrill, who co-wrote the script with Kevin Burke), 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. She is most often mistaken for Rachel Bilson from The O.C..