The 18-year-old Moroccan, whose real name is Karima El Mahroug, was paid 40,000 euros -- more than $55,000 -- to accompany Austrian real estate mogul Richard Lugner, 78, to the swanky event, which is the highlight of the social season, The Independent said.
Austria's elite has been scandalized in the past by Lugner's associations with young starlets. But this year his guest is the talk of the town -- and promoters of the ball are furious.
Opera Ball organizer Desiree Treichl-Stuergkh fumed that it was "the biggest embarrassment Mr. Lugner has ever created," according to the BBC.
Berlusconi was indicted last month on charges he paid for with Ruby when she was underage, then used his influence to cover it up. Both have said they did not have a sexual relationship.
"I hope that people will be able to react to me as they find me and not as 'scandal' Ruby," she said.
"I can only belly-dance. I can't waltz, but I will try and dance with the others -- you can learn a lot that way," she added.
As for Lugner, he seemed delighted by the stir his date was causing. "Her dance card will definitely be very full," he said, according to the BBC.