The former British royal has apologised after footage of her offering access to the Prince in exchange for $800,000 (£500,000) was released by British tabloid the News of the World on Sunday (23May10).
Ferguson was captured negotiating the deal with an undercover reporter, who was posing as a broker in the meeting.
The Duchess of York flew from London to Los Angeles on Sunday to attend the Variety charity gala, where she accepted an award for her work with needy children.
Ferguson skipped the event's red carpet, entering instead through a side door, but American Idol judge Cowell was there to fend off questions about the scandal.
He told reporters, "To be fair to her, she's a trooper. You know, she didn't have to be here tonight. She's very passionate about this kids' charity work she does and not many people would have done what she did (turn up) - but she did."
Ferguson hinted at her woes as she accepted the Catherine Variety Sheridan award for her "philanthropic achievements", telling the crowd, "Thank you all so very much. When I got on that flight today I thought, 'Phew, I've had a heavy day'.
"I learned today about making a difference. Most importantly I learned I hate grown-ups and I love children."