Linda Reynolds's position as Defence Minister has been labelled ‘untenable’ after the Western Australian MP extended her sick leave by nearly a month on Sunday.

Ms Reynolds has been plagued by scandal in recent weeks, after former staffer Brittany Higgins alleged she was raped in the Minister’s office in 2019.

The Minister took sick leave for a pre-existing cardiac issue shortly after, on February 24, as pressure mounted over the way Ms Reynolds and other senior ministers had handled the issue, and questions arose as to who knew what, and when. .

It has also been revealed Ms Reynolds called the victim a “lying cow” in front of another staffer when media reports began to surface about the alleged assault.

Labor senator Kristina Keneally said she hopes Ms Reynolds is making a full recovery, but blasted the Morrison government over two senior cabinet ministers being absent.

Attorney-General Christian Porter has been placed on mental health leave after self-identifying as the Minister being accused of a historical rape allegation.

“Her position is untenable,” Ms Keneally said on Sunday in regards to the Defence Minister.

“You cannot call the alleged victim of a rape in your own office a lying cow and think that has no consequences.”

Ms Reynolds said in a statement issued on Sunday that she would not be returning to her office on Monday, as originally planned, and had been advised by her cardiologist to extend her leave until April 2.

“Senator Reynolds has advised Prime Minister Scott Morrison of her doctor’s assessment and will continue to consult with the Prime Minister as required,” the statement said.

Foreign Minister Marise Payne will continue to act as defence Minister while Ms Reynolds is on leave.

“Senator Reynolds is recuperating well and looks forward to resuming her duties as Defence Minister as soon as possible,” the statement said.

Ms Reynolds has not publicly denied calling Ms Higgins a lying cow. Ms Higgins has also served a defamation lawsuit against the Defence Minister’s office, demanding an apology, which the Minister has made.

Ms Reynolds was expected to face questions in parliament and senate estimates in the next two weeks.

“Is the Minister of defence, Linda Reynolds, trying to pretend she is (on one hand) well enough to continue as Defence Minister, but not well enough on the other to front up and answer to questions in parliament and the (Senate) estimates?” Ms Keneally said.

Ms Keneally said she would welcome an independent investigation into the historical rape allegations made towards Mr Porter.

“This is the Liberal government that appointed an independent investigator … to look into allegations (that were) 30 years old about Julia Gillard, her former boyfriend and a kitchen renovation,” she said.

“If it is OK for the Liberal government to appoint an independent investigator to look into a kitchen renovation then surely it is OK for … the government to appoint an independent investigator to look into allegations of rape,” she said.