In the spring of 1981, when she was just 12 years old, Mary Lou McDonald was watching a news programme about the hunger strikes in Northern Ireland: "Anyone of my generation who saw those images of the H-blocks beamed into their homes was changed. For me it was the precise moment that I, as a Dublin girl, realised how seriously wrong something was.
"I completely understood and understand why people volunteered for the IRA. I support and recognise the right to meet force with force. Do I understand why volunteers came forward; was it necessary to take up arms against the British state in the north? I believe it was, even though I take no pleasure in saying that."
That sort of reaction would seem fairly understandable had she lived in one of the poorer, inner-city areas of Dublin, where the strains of A Nation Once Again might waft from the pubs.
But she didn't live there. She lived in the affluent suburb of Rathgar. She attended Notre Dame, the private, high-fees school in the even more affluent area of Churchtown. This was the sort of middle-class background that even the middle classes looked up to.
So, where did the republican, Sinn Fein, IRA sympathies come from? Was it just the standard teenage rebellion of a well-mannered, well-educated Catholic girl, going through the 'phase' of embarrassing the parents by adopting a revolutionary cause?
Or maybe she just didn't like the cutesy 'Mary Lou' name those parents had given her: because it's almost impossible to hear that name without being reminded of the song.
Actually, it goes much deeper than that. Her grand-uncle (her grandmother's brother) had been executed 'by the state' in the Curragh camp in December 1922.
"My grandmother never forgave or forgot."
McDonald was well-aware of that incident and equally well-aware of the effect it had had on her family, particularly her grandmother. Sitting in her very comfortable Dublin home in that spring of 1981, watching that footage from the Maze and hearing the views of northern republicans, probably awakened some very old, very dim understanding of her own family background.
Mary Lou McDonald was born on May 1, 1969. Her father, Patrick, was a very successful surveyor, married to Joan. She has two brothers: Bernard, a scientist and Patrick, a patent lawyer. Her sister, Joanne, is a teacher.
They were all high-achievers. After Notre Dame, where she gained a very good Leaving Certificate, she went to Trinity College to read English. Oddly – particularly for someone who has described the hunger strike as a sort of "road to Damascus moment" – she didn't get involved in student politics. Instead, she concentrated on her studies, taught English in Spain for a year after graduation and then continued her studies – in European Integration – at the University of Limerick. Her first formal link to politics was as a consultant and researcher with the Institute of European Affairs, a think-tank run by Brendan Halligan, the former Labour TD. Yet this was safe, almost middle-of-the-road politics: not the sort of radicalism one would have expected from someone so angered by the events of 1981.
So, maybe the rebellious phase had simply fizzled out and she would settle into the stereotypical middle-class environment which her education and upbringing had prepared her for?
In the mid-1990s, she married Martin Lanigan, who worked for Bord Gais, one of Ireland's leading energy suppliers. They moved to Castleknock, a suburb of west Dublin, and now have two children. Like many in Sinn Fein, she is fiercely protective of her family and rarely talks about them.
In 1998, she joined Fianna Fail, a move that pleased both her parents, who had long supported it. Given the fact that Sinn Fein was very much a minority interest in Dublin politics at that time, it seemed a sensible move for someone with her views.
Fianna Fail was still viewed as a 'properly republican' party, a party, moreover, which still appeared to be fully committed to the unfinished business of Irish unity. Again, given her background, it seemed the obvious first step to a safe seat and a long political career in 'the natural party of government'.
Yet she refused a nomination for a safe council seat a few months later, choosing, instead, to organise meetings about what was happening on the Garvaghy Road in Portadown: something which seemed utterly irrelevant to Fianna Fail's election needs in Dublin.
At the same time, she had opened up contact, north and south of the border, with Sinn Fein, and within a matter of months had defected from Fianna Fail.
She was a perfect catch for Sinn Fein, exactly the sort of person they needed: the sort of person who would normally have pursued a career in Fianna Fail. She was young, bright, articulate and attractive: "When I got politically involved, when I became active, I was looking for somewhere you could actually make a difference and Sinn Fein provide that space. There's a kind of stereotypical thing about what a Sinner should look like and that doesn't tally with the reality.
"I am not uniquely a middle-class person in Sinn Fein. I am not uniquely university-educated. We are a much bigger social mix than people might imagine."
Since then, her career has been constantly on the up (former MEP and now a TD and deputy leader of Sinn Fein), helped enormously by the fact that Gerry Adams "rates her and has a lot of time for her".
Indeed, some people believe she is his preferred successor. In some ways she is very like him: good at the mantras and unflinchingly focused messages, but not so good when it comes to detail.
On more than one occasion she has been mauled during interviews. But she is a clean pair of hands – a 'lilywhite', as they used to be known – and it is much harder for interviewers to distract her with personal questions about the IRA and her own past.
However much key figures within Sinn Fein – particularly in and around the media and political bubble of Dublin – profess their loyalty to Adams, it is increasingly clear they recognise there is 'a problem with Gerry'.
His past refuses to go away. The difficult questions about the IRA and the Disappeared refuse to go away. In interview after interview, he is forced away from questions about party policy and forced to defend himself.
Instead of being able to attack the other parties, he has to protect himself. And that is probably costing Sinn Fein votes: and it is certainly making progress and growth more difficult.
Step up, then, Mary Lou McDonald. Clean hands and good with the media. Loved by the party faithful and liked by the general public. Like Mrs Thatcher, not afraid to be interviewed while shopping for breakfast cereal in a Dublin supermarket.
Does she want the job?
"Not in the short term, but I wouldn't rule it out in the longer term. It's not something I'm concerned with now, but at some stage, if there were a vacancy, I would certainly consider it."
A perfect answer. No whiff of disloyalty to Adams and no whiff of sulphur in terms of coups, or internal manipulation. Yet not an entirely honest answer, either. She wants the job and Adams wants her to have the job.
It's hard to believe that they haven't already worked out the necessary choreography. Mary Lou McDonald is ready for the top job. She has unfinished business: the unfinished 'family' business of 1922; the unfinished business of her conversion to Sinner republicanism in 1981; and the unfinished business of the unity opportunities set out in the 1998 Agreement.
A life so far
* Born on May Day, 1969 and raised in the affluent Rathgar: she has two brothers and a sister
* She was educated at Notre Dame, a private fee-paying school in Dublin
* She had a "road to Damascus" moment in 1981 when she watched news about the hunger strikes
* She married Martin Lanigan in the mid-1990s and they have two children
* She joined Fianna Fail in 1998, turned down a safe council seat and then defected to Sinn Fein shortly afterwards
* She was an MEP, and is now a TD and deputy leader of Sinn Fein. Many believe she will be the next leader