But the Wanaka multisporter has twisted a workmate's arm to enter and has heard at least three women could be starting.
Williams insists Saturday is "not about winning.
It's about having people to do things with".
Being the only female entrant in any race is not a habit Williams (35) wants to get into.
She won the Central Otago Gold Rush in March with no female competition and her overall result against 17 men - she was fourth individual in 19hr 53min 53sec - was overlooked as accolades went to three-time champion Dougal Allan (24), also of Wanaka.
When Williams first received a call from the organiser of the Methven event, her heart sank.
"The only woman entered again? Why is that? It is a do-able event. It is only one day."
Williams surmises several factors could account for fewer women competing in the Gold Rush, such as time needed to train, the popularity of single-stage endurance races, or user-friendly triathlons, with one transition area and no need for support crews.
Prize money might also be a factor for the elite, but the Methven event is generous in this regard, as she points out.
And there are plenty of women pursuing the sport.
The Coast to Coast continues to attract big numbers.
Williams won from 65 finishers, in her first solo attempt at New Zealand's top multisport event.
Another 32 females entered the one-day event (25 finished). Knowing she had no female competition in the Gold Rush, Williams decided to compete against the women's teams, plus had a strategy to beat her kayak training partner, local GP Andrew McLeod, which she achieved.
She finished nearly 30 minutes faster than her first attempt in 2009, when she was second woman of five.
There was no multisport when Williams was growing up in Northern Ireland.
Home was Enniskillen, where Williams went to school, did "cross-country stuff", swam twice a week, and competed around Ireland and in Europe in "triathlons with horses".
"We would run a mile, swim as far as we could in three minutes and then go cross-country on horse, the most fun bit," she said.
Williams studied physiotherapy at Aberdeen University in Scotland and joined lots of sports clubs and the university's naval cadet scheme.
She moved to Edinburgh about 1998, bought her first mountain bike and ventured into the Glentress forest area near Peebles.
Then she went travelling, arriving in Wanaka in 2001.
When she returned to mountain biking in 2002, the Coast to Coast seemed a long way off.
Supporting a Canadian team in the now-defunct Southern Traverse several years ago was an eye-opener.
"They just didn't eat or drink. One of the guys ended up dehydrated.
"And if you are like that on day one, and you've got four days to go . . .
"I thought, This is dreadful. The poor thing."
By race end, she thought the Canadians were crazy.
They had been helicoptered off the course but went back into the mountains and got lost.
But she was not put off.
"It's just the thing you do here, isn't it?"
The Terrace Downs Defi on Saturday comprises a 30km mountain bike, 47km road cycle, 37km kayak and 15km run, based around Rakaia Gorge.
