Ms Harding, 38, is a teacher aide and mother of children aged 11, 14 and 18.
They live with her parents and she was the only smoker in the household - a moderate smoker on about 30 to 60 cigarettes a week - until she gave up at the start of the competition in March.
"I must admit the challenge is what really made me think about quitting ... I got asked to be the last one on the waka. I said, 'I will do it, it's for our marae,' not really thinking I would quit."
She used nicotine replacement therapy lozenges for three weeks but stopped because they tasted unpleasant. From there, she credits her success to changing her routine and sticking to the new one.
She had her first cigarette as a 14-year-old and "really started smoking when I got a job when I was 16". She quit smoking for each of her pregnancies and while each child was young, but always went back.
As her children have grown, they have encouraged her to give up smoking.
"Even in those first couple of weeks [of the competition] when I thought I needed a cigarette, they said, 'You don't need that.' They would always say, 'That wastes money.' They are really anti it."
Ms Harding said she now had no cravings for a smoke and felt better than before, physically and mentally.
She is saving money by not buying cigarettes, but spends it on food, because her appetite has increased since quitting smoking.
"For the first couple of weeks I was eating chips and packets of biscuits, whatever was in front of me, till I got into a routine."
She now eats a lot of fruit and has started going for walks with a friend at work.
The team's quit coach phones the members weekly to ask about progress and the team meet to support one another. Another form of mutual support for members is to blog on the competition website.
"People fall off the wagon, and that's fine," Ms Harding said. "There was no pressure to go cold turkey for everybody. It was a gradual process for some. There's a couple of us done it from day one, been smokefree totally. There are others that have had to wean themselves off.
"One of my aunties has smoked pretty much all her life. She is smokefree now after that first couple of weeks to reduce, and she has a husband who smokes. She had a harder time trying to quit with someone else that's still smoking all the time around her.
"I give it up to her because she's smokefree now and she feels great and it saves her heaps of money."