Ms Gibson, 35, began her weight-loss regime in November 2011, weighing 140.7kg.
"I averaged 1kg to 1.9kg losses every week and hit my goal weight of 75kg a year to the day after I joined Weight Watchers. It's about setting yourself little goals and not just focusing on the light at the end of the tunnel."
Last September, she completed a half-marathon.
"I am proud of what I've achieved. It shows people that it's not a pie-in-the-sky dream, that it is obtainable."
However, there was a downside.
"I've had people snub me because they don't recognise me any more.
"It also took a long time getting my head around going into shops and trying on smaller sizes. I've gone from a size 26 to a size 8 and I've had to change my wardrobe several times over. I hate to think what it has cost," she said.
"I've got a boot fetish now, too. I wear boots just about every day. I didn't used to be able to wear boots, because I couldn't do the laces up."
A South Island and North Island finalist will be selected at the end of the month to join five Australian finalists in Sydney for the slimmer of the year final in September.