Sarah Horn was invited onstage to perform an impromptu duet of "For Good" from the musical "Wicked" last weekend. Video of the performance went viral online.
Horn, who is from Riverside, has been invited back to the Bowl to guest judge the Abba Fest on Sept. 8.
The event will feature three Los Angeles-area collegiate a cappella groups: The Scattertones (UCLA), SoundCheck (Chapman University) and The SoCal VoCals (USC). The groups will perform ABBA classics, including "Take a Chance on Me," "Money, Money, Money" and "Does Your Mother Know."
Also, Swedish ABBA tribute band, ABBA The Concert, will close out the night with the band's greatest hits.