Incidentally, Tobin did meet that woman one day on the footpath outside her home to discover her husband was a "fanatic in everything".
"He said the two of us had to do something so 10 months after buying a pair of running shoes I did," Tobin says of her maiden marathon at Rotorua in 1981.
While the woman who inspired her didn't cross the magic 42.2km mark, little did Tobin know how that first foray would mould her life.
Around the 30km mark, Tobin had convinced herself she couldn't possibly put herself through that distance again.
"In those days no one walked the marathon so I said to myself once I finished the race I was going to throw my shoes into the Ohau Channel around Lake Rotorua."
The woman born in Pahiatua shrugged off her mental insecurities to instead follow her instincts to an enviable passage of achievements.
On November 3, the 65-year-old from Napier completed her 100th marathon - walking it in Feilding, which is championed as the longest-running one in the southern hemisphere.
Unable to run because of complications, Tobin is quite happy to have completed the marathon in 6hr 48min.
With a personal best time of 3h 39m 40s, she has run 75 of her 100 marathons.
So why did she change her mind in her maiden marathon where she clocked 4hr 50min?
"When you finish 42.2 kilometres it's not so bad," she says, drawing parallels with giving birth, after running her second in the Hamilton Marathon six months later.
"After the first one you say no more again but the next thing you know you're having another baby."
Marathons, she reckons, are hard work but you do not endure as much pain as childbirth.
Her daughter, Cathy Marshall, a maths schoolteacher from Tawa, presented to her a card to acknowledge she had officially clocked 42219.5km while another daughter, Natalie Marshall, was at the finish line in Feilding to greet her. She also received a medal and plaque from the organisers.
The events, she emphasises, have to be certified for distance officially to be recognised.
The girl, who hated sports in school and forever conjured novel excuse notes to try to get out of it ("there was no room for manoeuvring"), is now the fifth female to enter the exclusive New Zealand 100 Marathon Club of 33 in the country.
For the mother who went on to compete in 30 consecutive marathons, the formula is pretty elementary.
"You set it up and just kick over from one marathon to another," Tobin says.
"I don't buy into the adage of 'I don't have the time'."
Her advice to potential marathoners is that they simply have to get their families on side to fit into their training regime.
She has done eight in one year but, sometimes, had to settle for two due to other commitments.
The passion and endurance has taken her to 10 marathons overseas - in the United States, Finland, Hawaii, Australia, Japan and Puerto Rico.
The course that left an indelible impression was in 1995 in the US when they ran from Buffalo, across the Peace Bridge, to the breath-taking base of Niagara Falls in Canada.
It was, however, a logistical nightmare obtaining passports from US immigration authorities.
She feels Rotorua and the Hastings (around the Tukituki) marathons are her favourites.
The former simply because she did it with monotonous regularity until the tar seal and gravel took its toll on her body.
She recalls how in 1991 in Rotorua thousands of competitors were left distraught at the starting line as civil defence officials called it off due to rain slips.
The Auckland Marathon is the biggest in New Zealand in terms of numbers.
The toughest for Tobin, no doubt, was the one at Puerto Rico in 2003 when officials decided to carry on despite the thunderstorm and lightning. It had a field comprising marathoners from 70 countries as part of the World Masters Championship.
For women, of course, there was another overriding hurdle of convincing the world that females could hack the gruelling nature of the event.
Tobin fondly recalls how when she was a teenager, women were not allowed to run more than 800m in the 1960 Rome Olympics.
She draws immense inspiration from American runner Kathy Switzer, who lives six months of every year in Wellington.
Switzer, she reveals, registered as "K Switzer" in the 1967 Boston Marathon in a bid to pass off as a bloke.
"She cut her hair short and slipped on a cap to run with her boyfriend so everyone thought she was a man," says Tobin of the marathoner officials spotted on the starting line but couldn't stop from competing.
"Kathy's just an inspiration. She ran several times under three hours so she's like a legend to me and others," she says after meeting Switzer.
Running can be tedious for someone who didn't have the benefits of mobile electronic music gadgetry in her heyday.
She confesses to even day dreaming at times.
"You tend to think about things that happen in the world so you end up thinking about how you can change things or find solutions.
"Although when you've finished you've forgotten what all those things were that you were thinking about," she says with a laugh.
Primarily Tobin suggests beginners should entertain setting goals with motivational triggers.
"It's no good doing something random because that's where a lot of people fall down," she says, adding it's normal for aspiring marathoners to drift off every so often.
It has to have a wider appeal than just reversing, for argument's sake, one's health.
She finds comfort in the "active relaxant" theory of John Kirwan, former All Black and 2013 rookie Blues coach.
"What you put in is what you get out of it," says Tobin, who moved to the Bay in late 1988 when husband Jim Tobin earned promotion as a surveyor.
For the record, she will continue walking marathons.
"I'll be picking and choosing courses that suit me the most," she says with a chuckle.