Liberal candidate Georgina Downer has distanced herself from previous opinions about the GST and penalty rates in her first pitch to voters ahead of the upcoming Mayo by-election.

Ms Downer will be up against Rebekha Sharkie, who won the seat in 2016 as part of the Nick Xenophon Team but was last week forced to quit after being caught up in the dual-citizenship saga.

Ms Sharkie is facing an uphill battle to regain the seat with Ms Downer seeking to follow in the footsteps of her father, Alexander, who held Mayo from 1984 to 2008.

At her first press conference, Ms Downer indicated the views she held as an employee of the Institute of Public Affairs may not be the same she holds as a federal MP.

She distanced herself from previous comments that Western Australia is treated unfairly by the GST and that South Australia is getting more than its fair share.

"I was an employee of the Institute of Public Affairs, it's a think tank and it is engaged in a lot of policy research," she told reporters on Tuesday.

"As an employee of that think tank I articulated some of the policy views and these are important debates that we need to have in society."

When questioned about comments made in 2017 that Sunday penalty rates and the minimum wage be abolished, Ms Downer again said the comments were made as part of her employment.

"I think it's important to have discussions about these issues but ultimately the independent fair work commission has the authority, appropriately so, to determine those issues," she said.

Ms Downer said she moved away from South Australia after school to find job opportunities but as an MP would work to keep more young people in the state.

"I don't want South Australian girls at 18 years old to have to face that decision like I did," she said.

"I want them to have the education and job opportunities here in SA and particularly here in Mayo."

Federal Education Minister Simon Birmingham described Ms Downer as smart and capable and urged voters to judge her on her merits and not her family's relationship to the electorate.

But the minister also acknowledged she was up against a political precedent dating almost 100 years.

"Winning by-elections whilst in government is something that, essentially, is unheard of in Australia," he said.

"It's only once, back in 1920, that a government of the day has snatched a by-election from an opposition."

Meanwhile, Ms Sharkie said Nick Xenophon was busy rebuilding his life - caring for elderly parents and restarting his legal practice - and was unlikely to play a starring role in her campaign.

"I think I've already asked enough of Nick over the years, I think it's time for him to take care of himself," she said.