For the second time this year, Georgina Downer has secured Liberal Party preselection for the Adelaide Hills seat of Mayo — despite being soundly defeated in a by-election there six weeks ago.

Key points: Georgina Downer will be the Liberal Party's candidate for Mayo at the next federal election

Georgina Downer will be the Liberal Party's candidate for Mayo at the next federal election Ms Downer has again secured preselection for the seat, despite losing a by-election in July

Ms Downer has again secured preselection for the seat, despite losing a by-election in July A political analyst is predicting she will again lose to Centre Alliance MP Rebekha Sharkie

Centre Alliance candidate Rebekha Sharkie retained the seat in July with a comfortable swing towards her, after being forced to step down from Parliament because of the dual-citizenship saga.

Her victory came despite a highly public campaign by Ms Downer to win back the seat, which was held by her father — former foreign affairs minister Alexander Downer — for almost 24 years.

A ballot of party members was held near McLaren Vale south of Adelaide today, with Ms Downer seeing off a challenge from human resources manager Reagan Garner.

"There were initial problems with his possible Canadian citizenship which he claims have now been sorted out," University of Adelaide political analyst Professor Carol Johnson said.

"He certainly didn't have the sort of profile that Georgina Downer has even though there have been questions raised about the fact that she has been living away from Adelaide for so long."

The Liberal Party announced the result on Twitter, offering its congratulations to Ms Downer who, after the Mayo result, vowed to again become the party's candidate for the federal electorate.

"I am 100 per cent committed to standing in Mayo again next year," Ms Downer said in July.

"I'm proud of my family's commitment and service to South Australia … I'm committed to putting up a fantastic campaign for the next election as the Liberal Party's candidate if I'm preselected."

Ms Downer saw off a challenge from Reagan Garner for the Adelaide Hills seat of Mayo. ( Facebook )

Ms Sharkie now holds the seat on a two-candidate-preferred vote of 57.5 per cent after securing a 2.6 per cent swing in her favour.

The Mayo campaign was at times acrimonious, with Ms Downer's parents accusing Ms Sharkie's supporters of directing "horrible hate" towards their daughter.

Ms Downer initially won preselection in May, when she was endorsed unopposed ahead of the Super Saturday by-elections.

She was previously criticised for living outside the electorate, in Melbourne, where she lost a preselection battle ahead of the 2016 election.

Downer 'potentially vulnerable' on social issues

SA Labor wasted no time in retweeting the Liberals' tweet congratulating Ms Downer, but accompanied it with a mocking emoji of someone slapping themselves in the head.

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Professor Johnson said she was not surprised by the result, but questioned whether Ms Downer was the best choice for the party.

"She has very good links in the South Australian Liberal Party, she's well-known, she campaigned hard in Mayo at the by-election and she is a very bright and capable candidate with family links to the electorate," Professor Johnson said.

"In many respects she was the obvious choice, even though there are questions about whether she is actually the best candidate for this seat.

"It is a small 'l' liberal moderate seat in many respects and she is actually… from the conservative right of the party.

"Rebekha Sharkie in some respects represents the moderate Liberal vote better than the party's actual candidate does."

Professor Johnson said the next election "is likely to be fought on issues of inequality" which could work against Ms Downer.

"She is potentially vulnerable on a range of social and economic issues, especially because of past comments she has made," she said.

"She will be vulnerable because of some of the positions that she has raised regarding cuts to penalty rates and questioning whether we need a minimum wage."

Ms Sharkie now "stands a good chance" of retaining the seat, Professor Johnson said, because of public anger at the recent leadership turmoil that saw Malcolm Turnbull deposed.

Professor Johnson said Ms Sharkie could even secure another swing towards her.

"It's not entirely clear that some Liberal voters will have forgiven the current Government for what happened [to Malcolm Turnbull] and it's possible that that might actually increase Rebekha Sharkie's chances."