Preparing to defend the Hampshire seat she wrested from the Conservatives in a byelection shock a year ago, she warns her rival Tory candidate: "My campaign slogan will be: 'Paul Raynes, you are the weakest link. Goodbye.'"
The Lib Dems hope to be waving farewell on election night to Mr Raynes, a former Treasury high flyer and policy adviser to William Hague, as they did last May to the old Etonian farmer Tim Palmer.
In a byelection prompted by the death in a house fire of the Conservative incumbent Michael Colvin, Romsey pharmacist Mrs Gidley was catapulted to Westminster on an astonishing swing of 12.6%, overturning a Tory majority of over 8,500.
The victory, which followed an intensive Lib Dem campaign and a chaotic Tory effort, helped the new Lib Dem leader Charles Kennedy repel accusations of failure to make an impact, and caused severe tremors at Conservative central office.
At the coming general election, expected on June 7, the Lib Dems are desperate to consolidate an unexpected gain, while the Tories will be in deep trouble if they fail to recover a sprawling shire seat, stretching almost from Andover down to the Southampton fringes, that was previously regarded as natural Conservative heartland.
Some Conservatives regard the seat as a touchstone for Mr Hague's leadership - if it falls again the vultures may begin to circle. Labour's Stephen Roberts meanwhile will tacitly encourage supporters to cast tactical Lib Dem votes to keep out a Tory, while aiming not to go as far as his byelection predecessor and lose his deposit.
Tory postmortems have, correctly, concluded that the party picked the wrong candidate last time, having controversially rejected a local woman, Liz Perry, whom many feel would have comfortably held the seat. Barbour-clad Mr Palmer, who lived across the border in Dorset, came across badly.
But, despite the Tories' insistence that their problems were organisational rather than political, the party's policies - including tough talk on asylum and the usual emphasis on saving the pound - also played badly compared with conventional Lib Dem local fare, focusing on rural post office closures and hospital waiting lists.
A rain soaked rally in Romsey's pretty market square last April saw Mr Hague and the shadow chancellor Michael Portillo play to a damp crowd of supporters largely bussed in from other constituencies.
Mr Raynes, a key author of the Conservatives' Common Sense Revolution policy document, has common sense enough to stress that regaining the seat will not be easy: "The electorate has grown up, and no one is prepared to be taken for granted any longer."
Though the admission sounds astonishing in a constituency in classic Tory territory, the former mandarin is right that many natural Conservatives felt piqued that they had not been wooed but were merely expected to turn out.
Significant numbers stayed at home, contributing to the Conservative demise. "We recognise we could have tried harder when it came to turnout," Mr Raynes said. "There was a certain element of taking people, our own voters, for granted."
This time, he insisted, "the whole pace has gone up. Everybody is working".
Mr Raynes, 33, a sharp-brained high flyer with a personable doorstep manner and just a touch of the student politician about his orange jeans and University Challenge haircut, said he was determined to fight a positive campaign on "issues which matter" such as tax, bobbies on the beat and Labour's failure to deliver on public services.
"The Liberals will spend their time in Romsey demonising the Tories and demonising me," he said. "I'm going to run a resolutely positive campaign about making lives better for people by doing the things that they value."
Despite his protestations that his party would run a positive campaign, Mr Raynes was not above saying that Mrs Gidley was "immensely unpopular with an enormous number of people on both sides", adding: "She's not local, she's from Wales."
The MP was born in Monmouthshire but has lived for years in Romsey, while Mr Raynes, whose selection prompted the resignation of the Tory branch chairman who backed a local candidate, grew up in Surrey before living in London and Paris.
Welsh connections or not, Mrs Gidley enters an uphill election battle with the advantage of incumbency. Unlike Ms Robinson, she boasts an approachable manner. Her first year as MP has been spent in earnest Lib Dem backbencher fashion - she has made a solid Commons start while focusing on creating a strong constituency presence, popping up at parish council meetings, schools, hospitals and church services.
The Lib Dems will again use the two horse race ploy, urging Labour supporters to vote tactically for Mrs Gidley and dismissing Tory claims that last year's surprise was down to Conservative stay-at-homes.
Labour's Mr Roberts, a 40-year-old property businessman and supporter of voting reform, said helpfully: "Sandra is very popular with Labour voters, which makes my job more difficult."
For Romsey, as for much of the UK, Labour and the Lib Dems cannot calculate how big a role tactical voting will play in the next election. Both hope that, as the byelection appeared to signal, an anti-Tory vote still exists, with some voters even more prepared to think tactically now they know the strategy can have a real effect.
Some Tory votes may also be lost to the anti-EU United Kingdom Independence party, whose candidate Anthony McCabe, will hope to better the surprisingly low 901 votes the party took after an enthusiastic campaign last year.
A Tory-supporting antiques dealer a stone's throw from Romsey's ancient abbey, was among those questioning whether the Tories could really win the seat back. The youthful Mr Raynes, he suggested, was again not quite the right candidate for a seat desperate for a mature, genuinely local figure. "We hear nothing but Sandra Gidley this, Sandra Gidley that - we're sick of it, but at least she's getting about."
Mrs Gidley, pointing out that her suits are brown unlike Ms Robinson's stern black, travels the constituency wearing a green bracelet - the kind known as Buddha beads - bought for her by her daughter last year and said to represent success. "I hope it doesn't snap before the election," she said. Her link with Westminster may prove stronger than the Conservatives hope.
