One Nation helped get Labor's Susan Lamb elected in 2016 but Pauline Hanson doubts she'll get the same help at her upcoming by-election.
The Longman MP had a margin of just 0.8 per cent when she won in 2016, thanks to a strong flow of One Nation preferences.
But Senator Hanson is not inclined to tell her voters to preference Labor in the Longman by-election.
"I've got no time for Bill Shorten if he's going to be the future Prime Minister of this country because I don't trust him," Senator Hanson told Sky News on Tuesday.
"Hand on heart, I don't trust Bill Shorten."
Ms Lamb finally dumped her British citizenship on Tuesday, months after being told it made her ineligible to sit in parliament.
She is now eligible to run in the by-election, which can't be held until June 23 at the earliest.
"Susan Lamb is eligible beyond any doubt to run in the by-election of Longman and she will be an excellent flag-bearer," Labor leader Bill Shorten told reporters in Brisbane on Tuesday.
Ms Lamb was told last year she would likely have to resign, but she held on until last week when the High Court ruled ACT Labor senator Katy Gallagher ineligible due to her British citizenship.
Labor MPs Justine Keay, Josh Wilson and Centre Alliance's Rebekha Sharkie also resigned, while Labor frontbencher Tim Hammond quit for family reasons, triggering a total of five by-elections.
Georgina Downer, the South Australian Liberal candidate for Mayo, also revealed she renounced her British citizenship in September last year.
"I'd like to be an example to people that you can come back and have a fantastic life here," Ms Downer told reporters.
Her opponent Ms Sharkie may not get help from her former party leader Nick Xenophon, who she said was taking time out to look after himself.
South Australia's Liberals are also considering a move to dump one of their two women in the Senate, with Anne Ruston and Lucy Gichuhi potentially being pushed down the ticket.
The five by-elections have not been officially called, with Speaker Tony Smith still consulting over dates.