She qualified for the annual Hawaiian competition, to be held in October, after placing first in the 25-29 age group and being the first female and non-professional athlete to cross the finish line at the Asia-Pacific Ironman Championships in Melbourne last month.
The 27-year-old said she had come close to qualifying three times the last three years but injury had affected her training.
‘I was hit by a car two times in 2010 in the lead-up to the Busselton Triathlon, which left me with a broken collar bone,’ she said.
‘Despite being injured I raced anyway but unfortunately fell short of qualifying for the world championships.
‘Three years on and I felt confident and prepared mentally and physically going into the Melbourne championships.
‘I knew I was there to get a spot and that I had to win my age group to qualify, so I was pretty ecstatic with my results.
‘My sister Michelle was watching the race and told me I was in first position in my age group as I came off the bike, so I had a pretty good feeling then.’
The primary school teacher said the conditions on the day were terrible and that she knew it was going to be ‘one hard slog on the bike’ due to the windy conditions.
‘It was nothing I knew I couldn’t handle though,’ she said.
As a competitive person, Ms Duffield pushed through using ‘mind over matter’ to finally qualify to compete in the world championships in October.
She said that all the hours she put into training and competing over the years paid off that day.
‘I train with Michelle six days a week, with Sunday being our rest day,’ she said.
‘We train early in the morning and about two to three times a day.’
Ms Duffield said her twin sister Michelle and her are pretty on par when it comes to competing in triathlons.
‘I watched Michelle compete at the world championships in Hawaii in 2011 and I was gutted to not be competing with her,’ she said. ‘But watching her gave me a whole new determination in winning a place this year.’
Michelle is hoping to qualify for the world championships at a triathlon in the coming weeks in an effort to join her twin in Hawaii and compete together.