Senator Gallagher has denied she had misled parliament in 2021 about her knowledge of the allegation made by Ms Higgins before they were made public.
She said she did not seek to weaponise the allegations, and was responding to a claim she knew about the incident for weeks to use it for political gain.
As parliament resumes on Tuesday, coalition senators are set to use question time to target Senator Gallagher over her knowledge of the allegations.
Ms Higgins alleges she was raped by former colleague Bruce Lehrmann in Parliament House in 2019, a claim which Mr Lehrmann has always denied.
The trial of Mr Lehrmann was aborted over juror misconduct and prosecutors did not seek a retrial, citing concern for Ms Higgins' mental health.
The ACT is now holding an inquiry into the investigation and prosecution.
Senior Labor members have lined up to defend Senator Gallagher in the wake of the political storm.
Treasurer Jim Chalmers said the suggestion Senator Gallagher misled parliament was "absurd".
"Katy Gallagher has more stores of personal integrity than all of her Liberal and National pursuers combined," he said on Monday.
Mr Chalmers said she draws on "deeper reserves of personal integrity" than anyone he had ever worked with.
"The idea that these allegations about something that happened in a Liberal minister's office, in a Liberal government, is somehow the fault of the then Labor opposition is equally laughable," he said.
Questions were raised of the finance minister after leaked text messages between Ms Higgins and her partner David Sharaz emerged last week suggesting the pair contemplated strategising her story with Senator Gallagher, when she was in opposition.
Environment Minister Tanya Plibersek said accusations Labor had weaponised the rape allegations for political gain could deter other women from coming forward.
"What really worries me ... is if you are a young woman looking at the way this has unravelled ... you would really think twice about making a complaint," Ms Plibersek said on Monday.
"I really do want to send a message to those people who have been sexually assaulted or who are thinking about making a complaint, there will always be people who will stand up for you for your right to get justice."
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