The attraction?
"I've twice experienced at the end of a marathon what I would describe as the ecstasy that can only be replicated by childbirth."
Wow.
"It's a combination of endorphins, stress and the relief of getting there, which for me is exactly the same physical and emotional sensation I experienced delivering my babies."
She has twice crossed the line in "tears of ecstasy" - including at last year's Boston event minutes before it was fatally targeted in a twin bombing.
Ms Harre, a veteran activist and mother of two, is now attempting a run of another sort - an ambitious return to the nation's halls of power in a curious union with Mana Party leader Hone Harawira and Kim Dotcom.
Labelled by many a marriage of political convenience, Ms Harre admits it is unconventional. But the party's star-studded roadshows are attracting hordes of curious voters, with the packed-out events said to more closely resemble rock concerts than staid political hustings.
The day I catch up with Ms Harre for a run up Mt Eden she has just spent her first night at home with her family in 12 arduous days, but is off to Queenstown that afternoon for the next round of party events.
Home is a Mt Eden villa which she shares with husband Barry Gribben, who she describes delightfully as "a collector of languages". The pair met through the Labour Party - she joined at the age of 16, "how boring is that?" - and have shared a life of politics together.
Their house boasts leadlight windows and polished wooden floors. Fine red wines are stacked next to a bookshelf with Al Brown's Go Fish and Yotam Ottolenghi's Jerusalem cookbooks. An evocative work of art hangs above a huge ornate wooden table.
The former Cabinet minister greets me in black lycra leggings, fancy running shoes and a Rotorua marathon shirt. I tell the uncompromising left-leaning unionist a photographer is arriving shortly.
"I don't usually wear makeup running but I'd better put on foundation," she says, disappearing.
The couple moved in about two years ago after 17 years raising their family in Te Atatu. Ms Harre misses the old waterfront property's fantastic vegetable garden and prolific fruit trees. She is now trying to establish a "guerilla garden" in her new backyard, which has been "colonised by unproductive, non fruit-bearing foreigners".
She's obviously a foodie and loves cooking - Malaysian being her cuisine of choice, the spicier the better.
"I grew up in Fiji and was eating curries from the age of 3."
Enough small talk - we're off.
It's a beautiful winter morning with clear blue skies as we make our way up Ms Harre's street in the shadow of the mountain. With her punishing schedule there's little time for training runs these days and she admits her hopes of running the Queenstown marathon in late November have pretty much "turned to goo".
She'd need to be comfortably knocking off several 20km runs each week by the end of August - and there's little chance of that right now.
Ms Harre tries to eat healthily "on the road" and takes homemade muesli - "no fruit, just nuts" - wherever she goes.
It's the weekend before she squares off against Prime Minister John Key in the tightly controlled Helensville electorate debate. How does she feel?
"I'll rise to the challenge."
Ms Harre's had a few challenges over the years, what with that messy Alliance split with former comrade Jim Anderton; being diagnosed with breast cancer in 2011 and the subsequent double mastectomy.
But right now she's just focused on getting to the top of the hill.
"I'm doing quite well, aren't I?" she beams. I assure her she is.
Not that she should need any assurance from me. The wiry couscous lover has a stack of running trophies in her living room - she showed me - and has completed all five of her marathons in under four hours. Her personal best was 3:54.26, set in Wellington in 2012.
"That's how I qualified for Boston."
We snake our way up the dormant volcano amid a chorus of native bird song - the great city revealing itself as we near the summit.
She doesn't run with music. "It's a distraction from being in the world when you run.
"In my early days I would try and process problems. But in the last few years I've found it more a meditative process."
A sense of "freedom in the universe" is what she's after now - that and staying in shape.
"Obviously wanting to be fit and relatively less portly than most members of Parliament become, 'she said diplomatically'."
Will she name names? "I think their breasts speak for themselves."
Ouch.
She and Gribben part-own an organic vineyard on Waiheke Island which produces about 6000 bottles a year. She enjoys "working on the land". "It's a huge endeavour and it's sort of grown middle-aged along with us."
This year was supposed to be her "year off", she says. Spectacular fail.
In March she decided to take "deferred maternity leave" and headed to the south of France, alone, for an intensive month immersed in the language of love. She did nothing but learn French - her mother who died of breast cancer had spoken the language - and run.
The experience was rejuvenating and launched Ms Harre on another creative path.
"I came back feeling like all my neural pathways had been refired and I think that's what allowed me to be open to this opportunity."
What else is on Ms Harre's list?
"I've often thought about writing a book based on what comes out of running conversations.
"Particularly with women that I run with, often they become opportunities to work though a major issue at work - a psychopathic boss - those types of questions. In fact I'd say the psychopathic boss stories are probably the most prevalent [that] women share running."
Why on earth is that? "I have a theory that talking about problems when you're running is a bit easier than talking about them sitting across a table.
"People reveal all sorts of stuff about themselves when they're just in that relaxed running state."
I tell her it's a great idea for a book.
"That's copyrighted so Hollywood, you steer clear of my story."
If Kelston is her political turangawaewae, then the Waitakere Ranges is Ms Harre's spiritual running home. She has traversed its scenic tracks innumerable times on training runs over the years and speaks of the area with great affection.
"The Waitakeres are kind of like the fount of New Zealand running myth. If you run in the Waitakeres you're running in Arthur Lydiard land and you are running in the footsteps of heroes."
Our excursion is almost at an end. We jog back down her street, past a Labour Party billboard with a smiling David Cunliffe, and back on to Ms Harre's porch. She sheepishly admits she seldom warms down.
As I leave we both vow to get back into regular training. She grabs a bottle of Cabernet Merlot Malbec from her vineyard and shoves it under my arm, asking if it's ethical for me to accept. "Watch the Electoral Act Laila," her husband shouts from the next room.
I promise to declare it on the pecuniary register of gifts.
