At times, a mirror-image of her more famous central government leader just up the road in Downing Street, Porter, the Conservative head of Westminster City Council was an all-powerful, all-consuming figure.
Tough, hard, rich, she exuded a "can do, will do" image that left less ideologically committed colleagues and opponents trailing in her wake. Strident and straight-talking, she was a terrifying prospect.
Served by a loyal band of followers, Porter ruled over Westminster in a manner the like of which has rarely been seen in a British town hall. New York maybe, Chicago certainly - but not this country.
Much of what she did was good. Sitting cheek by jowl with Parliament, the borough of Westminster is what the Americans call, euphemistically, a "mixed neighbourhood".
From Victoria in the south to Paddington in the north, the area encompasses some of the richest properties in London and some of the poorest.
While no other place can match it for the power and influence of some of its more illustrious residents, Westminster also suffers from appalling deprivations. As a result, it is a highly strung political melting-pot, full of activists from both sides of the spectrum keen to impress their masters in the Commons.
With a fierce drive and energy, Porter went to work. Westminster applied for and received numerous grants, bureaucracy was pared, the council tax was made among the lowest in Britain, the streets were cleaned.
Westminster, with its new-found dynamism and energy, was held up as an example of what others could achieve.
While they dithered and squandered, Porter carved her own triumphalist way, even, controversially, ridding the council of three cemeteries for a nominal 5p each.
Now all that achievement has gone out of the window. Porter is at risk of being remembered for all the bad things: presiding over a council which embarked on a policy of political and social engineering, for allegedly supplanting social need with political ambition, for phrases that have a creepy, Orwellian 1984 feel: "designated sales", "building stable communities", and her very own, innocuous-sounding but actually dominant, strategic inner cabinet, the "chairmen's group".
Just how much mud will stick against Porter will not be known until the publication of the final report of the district auditor, John Magill, who was charged with investigating the allegations of gerrymandering: namely, that the council's housing policy was used to rig the borough in favour of the Tories.
Already, though, it is taking on frightening proportions. Mr Magill (whose inquiry is already in its sixth year and has so far cost more than pounds 3m) estimates that her policy of selling homes on the cheap in marginal wards and giving free house repairs for life lost the council pounds 29.9m.
That is the sum which Porter and nine other councillors and officials can expect to have to find if they are surcharged.
Not among them will be Michael Dutt, once consultant geriatrician at St Albans City Hospital and the Tory representative for Knightsbridge on Westminster City Council. In January last year, two weeks after publication of Mr Magill's provisional report, he shot himself.
His suicide note read: "My decision to end my life is due solely to the need to continue to fight this matter of designated sales, further draining my energy and requiring resources I do not have. I could not do my demanding medical work properly and without this I do not choose to continue living."
While Porter and her colleagues wait for Mr Magill - and he could do everyone a favour by getting a move-on, for theirs is an intolerable strain to be under - other questions are surfacing.
Another report is being prepared on the council's former Tory leaders. This second investigation, while it does not hold out the prospect of enormous immediate financial penalties, is no less disturbing - perhaps more so, if you believe that selling homes at a discount to likely supporters is one thing, but putting the homeless in potential death traps is another thing altogether.
The present Westminster administration has asked John Barratt, the former chief executive of Cambridgeshire council, to look into the decision, taken by Porter's "chairmen's group" in February 1989, to give the homeless a fresh start in two tower blocks in a Labour stronghold in the Paddington district.
All very laudatory. Except the two blocks, Hermes and Chantry Points, were built in the Sixties, in the days when slum clearance was to the fore and the dangers of asbestos, which was used in the buildings, were not appreciated.
By the time 100 homeless families were offered space in the partially empty 31-storey towers, asbestos and the fatal disease it causes, mesothelioma, were dread words - and the council knew it. But in the finely balanced political make-up of Westminster, the alternative to putting 100 families, who were likely to be natural Labour supporters, in a Labour stronghold was placing them in more marginal wards. This was, it would seem, politically rather less palatable.
Against such alleged gerrymandering, attempts by a local group to buy the flats - they would have removed the asbestos - floundered.
The flats have long since been boarded up and demolished. Asbestos litigation lawyers are standing by, their pulses sent racing by comments such as this from one former tenant: "If that had been a private landlord, I perhaps could have forgiven, but knowing that this was a council and knowing we were vulnerable people, in the sense that we were homeless and we had a little child ... allowing us to live with such danger is, to me, unforgivable."
Also standing by are Porter's legal advisers and supporters. Everything she did, they stress, was subject to careful legal scrutiny. "She never, ever, broke the law," said a Porter aide yesterday.
Others, though, are not so sure. They point to the "chairmen's group", and question whose interests it was serving: the council's or Shirley Porter's? At least one law professor, Martin Loughlin at Manchester University, is on record as saying the move to Hermes and Chantry was unlawful "because it was an attempt by the 'chairmen's group' to harness the resources of the council for party political ends".
Now spending much of her time in Israel, Porter remains defiant and angry.
"She is astonished," said her friend. "She is astonished that anyone could think she would ever do such a thing. She has done nothing to be ashamed of."
That may be so. But what she has done has left the Government with a huge question-mark that refuses to go away. Once local government was Labour's problem, now it is also the Tories'. From heroine to embarrassment, Dame Shirley's fall has been total. ( Graphic omitted )