Less than a week after her surprising smash performance at the Hollywood Bowl last Friday, voice teacher Sarah Horn is preparing for her second appearance at the venue.

Horn, 26, will guest-judge the Sunday, Sept. 8 ABBA Fest sing-off between three local university a cappella groups: the Scattertones of UCLA, SoundCheck of Chapman University and the SoCal VoCals of USC.

And there may just be an encore performance in the works, hinted Horn.

"This is just a dream come true -- very, very fast," said Horn to the Huffington Post in a phone interview. "It was such a last-minute addition that I don't even know if I will have a bio in the program. We're still working out the details."

For Horn, who lives in Riverside and teaches at California Baptist University, the past few days since performing "For Good" with Kristin Chenoweth has been a whirlwind. There have been numerous media interviews and dozens of congratulations notes from friends. But what's been most amazing for Horn to see are the deluge of messages from strangers who have stumbled upon the viral YouTube video of the performance (now at 2.5 million views and counting), and been inspired by the song.

For instance, Horn's own former voice teacher from junior high school got in touch to say that Horn's Hollywood Bowl performance inspired her to re-prioritize her own vocal training, in addition to teaching 45 students a week.

And a grieving father who lost his infant son got in touch with Horn as well, to say that since the song "For Good" played at the funeral several years ago, he hasn't been able to listen to it since because of how sad it made him. But Horn's performance made him feel something other than grief this week. Horn read his Facebook message aloud:

"He said, 'I felt the tears come streaming down my cheeks, but this time, I felt joy,'" recounted Horn. "More importantly, I felt my son in my heart again, and I haven't felt that in a very long time. You made a difference in a grieving dad's life, and he's been changed for good."

It's messages like those, said Horn, that have continued to build on the inspiring experience she shared with Chenoweth in the first place.

"That really touches my heart, and it's what inspires me to keep going when the world keeps piling on," said Horn.

The ABBA-Capella competition will end with a performance from ABBA tribute band ABBA, The Concert. To learn more about how to get tickets to the event, check out HollywoodBowl.com or Ticketmaster.com.

Last Friday, Horn was plucked from the audience to sing the duet "For Good" with Hollywood Bowl performer Kristin Chenoweth. The pitch-perfect rendition shocked and amazed Chenoweth, as well as electrified the venue. A YouTube video of the performance also went viral.

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