"I think maybe a lot of women don't enter because they think they haven't got the cheque book to follow it through, but you don't have to spend a fortune to be a competitive force in racing fashion," she said.
"It's about taking current fashion and racing trends and working with what's available in the high street stores and putting your own individual stamp on it."
Her tip for entrants was to wear something that would help them stand out, while still keeping with their personal style.
And after a six-year hiatus, she will be competing for today's top spot.
"I'm going to give it a go - you've got to be in to win, and it's a really nice event to be part of."
She said it wasn't overly competitive and it was a great way to meet new people.
"A lot of the women who do these events regularly, you get to know them and you become friends.
"It's a lot of fun. It's been a really long time for me, but you miss it, and it's enjoyable for me. It's nice to have the opportunity to dress up and really put some effort into your outfit."
And though she was not willing to disclose today's attire, she did let slip that her hat was home-made.
Since entering and winning her first competition at Ellerslie on Boxing Day 2006, Ms Hahn said she'd caught the racing fashion bug.
"It kind of stirred an interest for me.
"It's a really fascinating fashion subculture and it's becoming increasingly popular here, though it's just a drop in the ocean compared to the numbers in Australia or Ireland."
Despite the lower numbers, she said the standard in New Zealand was up there with the best, as evidenced by last year's winner Olivia Moor taking second place in Melbourne.
This year's national winner will receive a bumper prize pack, which includes a trip to the 2015 Melbourne Cup Carnival and entry into Myer Fashions on the Field.
On the judging panel at Ellerslie this year will be Australian milliner Kerrie Stanley, TV3's head of makeup and styling Tracey Dalton and Viva beauty editor Janetta Mackay.
Racing 101
February 28 - TV3 Derby Day:
When?
Gates open at 10.30am, with the first race about 12.25pm. The New Zealand Derby is about 5.48pm.
Where?
Ellerslie Racecourse, 80 Ascot Ave, Auckland.
What?
10 races, including the New Zealand Derby. Total stakes $1.21 million. Viva Prix de Fashion - New Zealand's Fashions in the Field final. Picnics and Ponies family area with free children's entertainment including pony rides, bouncy castles, Popsicle Planet and swingball. General admission $10. Children under 15 free.
Fashion forward
• Tips for fashion in the field events from Viva Prix de Fashion judge and top Australian milliner Kerrie Stanley
• Millinery will make or break a winning outfit - silhouette and proportion are essential. For example, a fitted dress can take a dramatic headpiece while a full skirt can be balanced with a classic brim.
• Don't be afraid to embrace colour. Feature a tone from a patterned outfit in your accessories. Wearing black? Pop it with an accent of colour.
• Ensure your millinery is well secured to your head and pack extra hair grips (bobby pins) and hair spray. Think sleek, editorial looks for your hair: low ponytails, chignons and fishtail braids. It's all about balance.
