"It was unexpected, that's for sure."
The 33-year-old lawyer, who specialises in family court and law, decided to compete this year after a long break from the races' fashion competitions.
"Mum and I used to do the fashion at least 10 years ago," she said.
Ms Marshall had entered two other fashion competitions, picking up the style award at the Riccarton Races, but the competition at Ellerslie racecourse was tough.
"I'm pretty chuffed, the standard is pretty full on," she said.
"It's like another world."
It took her approximately an hour to get ready for the big day, which took around three hours to complete.
"We pottered over, and it started at two and was announced at five," Ms Marshall said.
She estimated she spent about $500 on the outfit, with the winning dress arriving only a week and a half before the races after she bought it on the internet.
"I literally only got it 10 days ago, it was do or die if it didn't fit," she said.
Ms Marshall won $3000 of Tous jewellery, which she would probably spend on her mother, she said.
By winning the Supreme Award she gained automatic entry to the Auckland Cup Day's fashion competition in March, where the overall prize is $30,000.
"I'm not sure what I'm going to wear. I'll have to do some homework," Ms Marshall said.
Judge and stylist Sammy Salsa told NZ Herald Ms Marshall was "a classic beauty".
"It looked like it was effortless," Ms Salsa said.
"I love the colour, it's beautiful and very in - not just in race wear but in fashion."
