"My partner and I decided we were going to do something amazing for our 50ths," said the 49-year-old.
"He chose to do the Lake Taupo Cycle Challenge and I decided to do the Ironman."
They have taken part in two smaller triathlons in the lead-up as preparation for Ironman New Zealand.
The biggest hurdle to overcome was the not insignificant fact that du Toit could not swim.
"I had to learn how to swim. I couldn't even do the swims in the triathlons to begin with but now I can.
"It's become our life to be honest. It's been amazing and life-changing."
Du Toit will be competing in Taupo with her partner Bob and her sister Jenny who is a personal trainer.
"We train almost every day, sometimes twice a day.
"My sister and I have very similar times in training but we don't have any time goals, we all just want to finish. We know it's going to be a long day."
Du Toit and Jenny will be two of 433 women in a record field of 1750 competitors, females making up more than a quarter of the field.
"When the event moved to Taupo some key advantages were that the course was more athlete-friendly and we could extend to the 17 hour cut-off," said Janette Blyth, the Ironman New Zealand Event Director.
"As an organisation we worked closely with event operators who focused on entry-level activity and created the pathway for women in particular to venture. That has resulted in an increase where women now make up over a quarter of the field. We would like to see that continue to increase and will continue to work hard to support active and healthy lives.
"Ironman is life-changing, it is a lifestyle and with Ironman, anything is possible."
The finish line is going to be an emotional place for her.
"I hope I can celebrate my birthday at the finish line and watch some fireworks. "My daughter and granddaughter are coming in from the USA to watch the event. Other family are coming to Taupo to watch too.
"It's the most amazing and exciting thing I've ever done," she said.
Ironman NZ
• When: Saturday March 1, 2014.
• Where: Lake Taupo.
• Event distances:
• Swim 3.8 km
• Bike 180km
• Run 42km
Men's Pro Records
Swim 44:47 Brent Foster (NZL) 2004
Bike 4:26:45 Steve Larsen (USA) 2003
Run 2:42:01 Claus Bjorling (SWE) 2004
Finish 8:15:34 Bevan Docherty (NZL) 2013
Female Pro Records
Swim 46:30 Monica Caplan (USA) 2005
Bike 5:01:17 Emi Shiono (JPN) 2008
Run 2:59:11 Jess Dracsau- Petersson (GBR) 2004
Finish 9:14:35 Joanna Lawn, (NZL) 2010