Horn, a Cal Baptist voice teacher and musical director of Riverside Youth Theatre in California, will guest judge the Bowl's ABBA-Cappella competition Sept. 8 at 7 PM.

The contest features three Los Angeles-area collegiate a cappella groups: The Scattertones (UCLA), SoundCheck (Chapman University) and The SoCal VoCals (USC), who will compete in a show-tune-styled sing-off of ABBA classics. Song selections include "Take a Chance on Me," "Money, Money, Money" and "Does Your Mother Know," and the groups will be judged based on audience applause.

"All three groups compete in the International Championship of Collegiate A Cappella (ICCA), the foremost competition for college a cappella groups, and enjoy a friendly cross-town rivalry," press notes state. "The Hollywood Bowl sing-off pins the three high-achieving groups against each other once again, showcasing first-rate singing and choreography through original arrangements."

Horn was selected from the audience to duet with Chenoweth on the song "For Good" at the Broadway star's Hollywood Bowl concert. She impressed the audience with her singing skills, and the YouTube video of her performance has reached two million hits.

Horn will perform at the ABBA-Cappella competition along with Waterloo, the Swedish ABBA tribute band.

Tickets are available by calling (323) 850-2000 or visiting HollywoodBowl.com.