Small, dark, direct, with an at times wickedly irreverent sense of humour, she is set to become Permanent Secretary at the Department of Social Security at the end of September, responsible for a pounds 90bn budget at a time when social security spending is the eye of the storm in the debate about the future of the welfare state.
The former Reading council estate girl will join Sir Robin Butler, the Cabinet Secretary, in weekly top mandarins' meetings - becoming, by far, the most senior of Whitehall's three female mainstream permanent secretaries. The others are Barbara Mills, the Director of Public Prosecutions, and Valerie Strachan at Customs and Excise.
Aged 57, Mrs Botwell's career started in the pre-DSS National Assistance Board in 1960, before moving to the Department of Health in 1990. In 1992 she became First Civil Service Commissioner. On the way, she has had four children.
Returning to head the Department of Social Security, she admits, feels "very much like coming home". Her first jobs were in South Shields and in inner London's St Marylebone back in the days when they sent the fast- stream high flyers out into the field to experience social security at the sharp end.
"It was a very good introduction to what it was all about," she says. In South Shields she worked the "order book bonking machine" - the contraption which stamped out the benefit books in the days before computers produced Giros. In Marylebone, she worked in the local office for four months.
"That was an eye-opener. I'd been brought up on a council estate, but I had been at the polite end of the market. I just hadn't seen poverty and deprivation of that sort, and it doesn't leave you, even if you only do it for a relatively short time."
Her talent was spotted from the start, and a Civil Service which had only just dropped the "marriage bar" as she joined - the requirement that women civil servants resign on marriage - found itself having to adapt to keep her.
Unusually for those days, she was allowed longish maternity leave and to work part-time for a decade, even persuading the Treasury to change its rules to allow her a year off unpaid when her husband, an advertising executive, took a job in the United States.
It produced moments of farce. As late as the early 1970s, part-timers couldn't be promoted. "So at one point I went full-time, got promoted and had another baby so I could go part-time again - it got quite ludicrous," she says.
Whitehall has, of course, had female permanent secretaries in big-spending departments before - most notably Dame Evelyn Sharp, head of housing in the 1950s and then of the Department of the Environment. Harold Macmillan called her "without exception the ablest woman I have ever known".
Although Mrs Botwell didn't know the Dame, she says: "I had a lot of female role models when I was young in a way I suspect people in other departments generally didn't."
There was an under-secretary and an assistant secretary in the National Assistance Board when she joined, and later there was Mildred Riddlesdell, who like Mrs Botwell was the social security permanent secretary at DHSS at the turn of the 1960s.
"It didn't occur to me that women couldn't get into senior positions - I just didn't notice that they were all single and childless, but they were."
The Civil Service unions, who dealt with Mrs Botwell when she handled personnel, first in social security and then in health, rate her, as does everyone else, as "quite a toughie". She's a woman of directly delivered opinions and the sort of organising ability you would expect from someone who has run a career and brought up four children.
A former colleague says: "She can be sardonic, acid, and very, very funny, but she is never arrogant. She was always reluctant to be promoted, almost distrustful of her own ability before making a roaring success of every job she did."
An unrepentant twang of south London remains in her voice despite Girton College, Cambridge, and years in the senior Civil Service.
Tough she may be. But she also inspires remarkable affection. Ministers who haven't worked with her for a decade still send her Christmas cards and two former permanent secretaries, knowing she was going to be interviewed, volunteered without affectation: "Do give her my love." Her battle honours include sorting out the Finer Committee on One-Parent Families which became so disastrously bogged down that after three years' work there was no sign of even a draft report. She was sent in to get them to write a final one, and did so.
She helped design child benefit in the mid-1970s, and in the mid-1980s she ran the key central co-ordinating unit for Norman Fowler's vast social security review.
As it started, she told him bluntly that she had two tests of whether he was serious: getting rid of the universal, and by then almost valueless, pounds 30 death grant, and abolishing the miserly 25p addition to the over-80s pension. He passed one and failed the other.
As First Civil Service Commissioner she banned a procedure where ministers had started interviewing permanent secretary-level candidates for agencies and expressing their preference before the Civil Service interview.
That row came to a head with Kenneth Clarke's controversial appointment of Derek Lewis to head the Prison Agency. She let her decision be known with the dry comment that the process "had not commanded confidence".
Michael Bett, her successor in a role given new independence and powers, "owes her a lot", according to one Whitehall insider. "She's a one-off," a former colleague said. "Almost uniquely these days, she knows the history of the benefits system but she isn't trapped by it. It is a formidable job. But she's a formidable lady."
Her own view of her own child-caring career was that it was hard, though she says,"it didn't feel hard at the time, because that was just the way it was".
She supports the saner dispensation which came in from the late 1970s onwards, but says it will take time for significant numbers of women to reach the top.
Despite this, she says "nothing can overcome the difficulty that it is actually quite hard to work with children. You still have the problem of what you do if they are ill and whether your partner will help - nothing makes that go away. Mine did, and it's another reason why I am here today."
If all goes well, she will become a Dame - the female equivalent of the Whitehall knight. "You can just hear her laughing at that," one friend said. " 'Me? A Dame'?"