Catriona, a nurse at the Mater Hospital in Dublin, was wearing a white fitted dress by Bastyan and a floral Mary Katrantzou cropped jacket.
She topped off the feminine look with a pink headpiece from Irish milliner Mark T Burke.
The judging panel for the Irish Derby was led by TV star Milile Mackintosh and included Image magazine's editor Melanie Morris and Stacey O'Donnell, Head of Personal Shopping at Brown Thomas.
Catriona's prize, worth almost €20,000, includes a luxury trip to Dubai, a personal shopping experience at Brown Thomas and a gorgeous diamond pendant from Boodles.
She commented on her win: “I’m completely over the moon to win such an amazing prize. I can’t wait to book my trip to Dubai and to pick up all my holiday goodies at Brown Thomas! My husband Jason is an Engineer in Saudi Arabia so I can’t wait to spend time with him in Dubai.”
Milile Mackintosh looked chic in a dress and bag by Victoria Beckham, shoes by Kurt Geiger and a head piece from Irish milliner Mark T. Burke.
She said on picking a winner: “The competition was really strong at the Curragh today and the standard was in a league of its own, the judges and I were really looking for something unique and I think we found it in Catriona’s look.”