It's never the ones you expect, a wise former head of HR once told me: never the seemingly unambitious or semi-detached who quit to see more of their children. It's the alpha females, the ones who couldn't bear not to shine at everything, couldn't stand the inevitable domestic and professional compromises.

So perhaps it's not so surprising that Louise Mensch is joining the ranks of the disappeared, those political parents leaving to spend more time with the family, alongside Ruth Kelly and Alan Milburn (for yes, men occasionally do this too). But to react by trampling over the old familiar turf – can parents really cut it at the top, shouldn't Commons working hours be changed? – somehow feels like missing the point.

Like almost everything she does, Mensch's resignation divides opinion. Tories will be exasperated at having to fight a byelection in a recession; Labour thrilled that Corby's slender majority is there for the taking. Those who feel she shouldn't have entered the kitchen if she couldn't stand a full five years of heat are furious: among parents, there is variously dismay at another high-flyer biting the dust, sympathy from the equally agonised, and resentment from those who can't afford to quit.

But love Mensch or hate her, don't buy the line that she merely got bored and flounced: for whatever else she achieved in politics, she was never exactly stuck for ways to make it interesting. And the lesson I learned three years ago, when I quit my own job as the Observer's political editor and began interviewing other parents who had made similar decisions, is that these things are rarely as simple as they seem.

I don't doubt Mensch was genuinely torn. She has felt her responsibility to her three children fiercely, particularly since her divorce from their father, stretching herself thin to be the kind of mother she felt she should be. Unusually for an MP, she chose not to have a full-time nanny, but to work from home as often as possible instead (a tactic revealed when she infamously left a select committee interrogation of Rupert Murdoch early to do the school run).

And while she knew when she was selected what the job would entail, her home life has become infinitely more complicated since then. She and her husband separated three years after she became Corby's candidate, and although she recently remarried, her new husband lives in the US. While many Westminster parents face painful choices over where the family belongs (school the children in the constituency and you won't see the family all week: in the capital, and the constituency association may bitterly complain), Mensch was ricocheting in a demented triangle between London, Corby and New York.

No wonder she made her name on Twitter, not in the chamber: working parents are blissfully weightless on social media, since you can tweet anywhere – children on your lap if necessary – with nobody the wiser.

But it probably couldn't work for ever, and now it hasn't. She's made her choice, one perhaps as much to do with marriage as with motherhood: not for her the dutiful spouse, picking up domestic pieces and opening church fetes in her absence, without whom many more political careers would founder.

It's fair to wonder, of course, quite how satisfying her career had become. The ambitious working mother's exit often conceals reservations about the next step up the ladder, which help tip the balance towards the eternal guilt about the children.

For all those glitzy photo spreads, Mensch was never less than serious about politics and fancied a shot at the right department (though one somehow can't see her grinding away in obscurity as a junior Defra minister). But she must have known the juggling act would only intensify had she become a minister – and that on the Tories' polling numbers, MPs in marginal seats risk oblivion in 2015. Was it really worth another three years of frantic juggling, only to be left with nothing to show for it?

So with hindsight, the social media business she recently established in the US looks like an escape route: and whether or not it succeeds, I doubt she'll sit around making cupcakes. The chicklit novelist who reinvented herself as a politician is quite capable of reinventing herself again.

As for the hoary old question of what this means for the work-life balance debate, Mensch herself is quite clear: nothing. She has rather admirably declined to have her personal choice turned into propaganda for the "told you mothers can't hack it" brigade, telling her local paper that another woman might well have managed but she simply decided not to.

She's right to say that what suits one parent cannot be assumed to suit all others. But she's particularly right because her own circumstances – the transatlantic marriage of two wealthy professionals in unusually all-consuming jobs – bear almost no relation to those of the average working mother, struggling to pay the nursery bills.

So Mensch is best remembered not as the poster girl for not-having-it-all but as simply as a law unto herself: the politician who thwarted a tabloid exposé of past drug-taking by happily suggesting they didn't know the half of it; the outspoken Tory feminist when the F-word was still taboo in her party. Politics will be duller without her. But perhaps now we can talk about the unglamorous childcare challenges that matter.

Gaby Hinsliff is a former political editor of the Observer