Malcolm Turnbull has paid tribute to the retiring minister for jobs and women, Kelly O’Dwyer, describing her as a “true liberal” who “demonstrated women can do anything”.

O’Dwyer’s shock resignation on Saturday has sparked further debate about the low representation of women in the Liberal party and the difficulty for senior parliamentarians of balancing work and family commitments.

O’Dwyer announced she was not recontesting the next election due to the “very personal reasons” of wanting to spend time with her young children.

The Labor leader, Bill Shorten, has argued O’Dwyer’s departure will heighten instability in the government and warned the Liberals may be left without any women in the lower house in Victoria if O’Dwyer is not replaced by a female.

Several candidates have already expressed interest in the ordinarily safe Liberal seat of Higgins – with the unsuccessful candidate for the state seat of Prahran, Katie Allen, confirming she will run and Victorian senator Jane Hume also likely to attempt a shift to the lower house seat.

The Liberal party is keen to preselect a woman after the defection of MP Julia Banks to the crossbench, Jane Prentice losing preselection and the retirement of marginal seat holder Ann Sudmalis drew attention to the low representation of women in the party.

Peta Credlin, Tony Abbott’s former chief of staff who was forced to rule out a tilt against O’Dwyer in 2017, could “clear the field” if she contested, according to one Liberal powerbroker, because she is popular with older Sky News-watching members.

Scott Morrison told reporters in Melbourne it was the party’s decision but “I believe, yes, she will be replaced by a woman”. “I’m very confident about a very strong female field,” he said.

Despite the public pressure, there is nothing to stop a man – such as Malvern Liberal heavyweight Greg Hannan or City of Port Phillip councillor Marcus Pearl – contesting the preselection, a move which could see a repeat of Wentworth where Dave Sharma was preselected despite calls for a female candidate.

At a press conference on the Sunshine Coast, Shorten said he respects O’Dwyer’s decision but “losing a cabinet minister, no matter what the reason … just heightens the instability”.

Shorten speculated that more government members could “just [say] they’ve had enough, pulling the rip-cord and getting off the government aeroplane”.

The Liberal party is bracing for the possible resignation of its former deputy, Julie Bishop, who quit as foreign affairs minister after she was overlooked for the leadership and has not committed to stay on after the 2019 election.

Labor’s deputy leader, Tanya Plibersek, who has raised three children while in parliament, said she understood the pressure O’Dwyer was under.

But Plibersek said the Liberals had failed to make juggling motherhood and ministerial duties any easier.

“One of the differences the Liberal party could make to make it easier to retain people like Kelly O’Dwyer on the frontbench is increase the number of women in their parliamentary party,” she told reporters on Sunday. “Because when you get a critical mass, it does change the culture.”

Morrison said he was “disappointed” at “churlish” behaviour from Labor towards O’Dwyer, arguing it was a “deeply personal” decision for members to retire.

“How about you just give them the benefit of the doubt that they’re [making that decision] for the reasons they’re saying?”

On Saturday evening Turnbull thanked O’Dwyer for her service, describing her as “committed to fairness and opportunity” while “never losing [her] passion for economic reform”.

Thank you Kelly. You are a true liberal, committed to fairness and to opportunity, never losing your passion for economic reform. We could not have achieved so much reform in taxation and in financial services regulation without you. 1/2 — Malcolm Turnbull (@TurnbullMalcolm) January 19, 2019

Turnbull highlighted her record as the first woman to hold a treasury portfolio in cabinet, and noted she was also a trailblazer to do so with “such young children”.

You have demonstrated women can do anything - including first woman to hold a Treasury portfolio in Cabinet and certainly the first to do so with such young children. The Parliament’s loss is you, your family’s (and your sanity’s!) gain. Good luck dear friend and thanks! 2/2 — Malcolm Turnbull (@TurnbullMalcolm) January 19, 2019

O’Dwyer – a protege of the former treasurer Peter Costello and loyal supporter of former prime minister Turnbull – is a moderate Liberal representing the inner-city Melbourne seat of Higgins, which she holds on a margin of 8%.

But what was once a prized safe Liberal seat will be difficult to hold in the 2019 election, after the replacement of Turnbull with Morrison and the Coalition’s landslide defeat in the Victorian state election expanded Labor’s list of target seats in the progressive state.

In a crisis meeting following the brutal Victorian election, O’Dwyer reportedly said the Liberal party was struggling because it is viewed as “homophobic, anti-women, climate change deniers”.

In December internal Labor polling of 550 voters in Higgins suggested Labor could win the seat with a two-party-preferred vote of 52%.

On Sunday the veterans affairs minister, Darren Chester, told ABC News Breakfast it was “hard to see” how the demands on a cabinet minister could change to better accommodate family life, citing his own experience of spending 200 nights away from home during his 20 months in cabinet.

“You sign up for these jobs,” he said. “You want to be able to make a difference, affect the country’s and region’s future. You get the good and the bad with that.”

Chester said politicians were expected to “get out there and talk to people” and that meant they had to “do the hard miles”.

“I’m sorry, there’s not much else we can do about that.”