Fairfax Media understands Ms Mills has accepted an invitation by the finance and public administration committee, chaired by Liberal senator Cory Bernardi, and will likely appear on Wednesday of budget week.

As the now former secretary of the Department of Parliamentary Services, she was not compelled to attend and her acceptance has surprised some given the ferocity of the interim findings the committee made against her.

It was those findings, released last week, which shed light on why House of Representatives Speaker Bronwyn Bishop and Senate President Stephen Parry fired Ms Mills.

Ms Mills has been at the centre of a number of controversies. News that she had been earmarked for the top job at Britain's House of Commons led to a furious backlash among British MPs and derailed the move.

The announcement of her termination in Canberra came in a two-line statement from the presiding officers and Ms Bishop and Senator Parry have declined to comment further.

But the committee's 40-page interim report into the department raised a number of serious allegations and branded the department under Ms Mills' management as "deeply dysfunctional".

Committee members were incensed to learn that recommendations dating back to 2012 to improve the department had remained largely unimplemented on Ms Mills' watch. A recent damning report by the Australian National Audit Office, which highlighted deficiencies with the management of assets and contracts, added to the pressure.

"Unfortunately, given that DPS has thus far been unable to implement the committee's recommendations from 2012, the committee holds little hope that DPS will be able to effectively implement the ANOA's recommendations," the interim report said.

But it was two episodes during her tenure - and her subsequent version of those events - that led the committee to declare it was misled and has "no confidence in the evidence provided to date by Ms Mills".

The first matter was the department's use of CCTV footage of a staff member who leaked material to former Labor senator John Faulkner.

At an appearance in front of the committee in May 2014, Ms Mills said she had only become aware of any issue around the use surveillance footage that morning. But evidence gathered by the privileges committee, including from Ms Mills' in-house rival, Clerk of the Senate Rosemary Laing, cast doubt on that statement.

Ms Mills lashed out at the committee in February, arguing she had been denied procedural fairness and natural justice, and that the senators relied on dodgy advice from Ms Laing. She is expected to again defend her actions when she fronts the committee again.

The second matter was the department's commissioning of artist Anne Zahalka to commemorate the 25th anniversary of the opening of Parliament with a photo essay of workers in and around the building.

Zahalka, who was paid $30,000 for 10 works, is a neighbour of Ms Mills in the inner-west suburb of Newtown. Under questioning, Ms Mills revealed she had spoken to Zahalka about the commission at a street party in 2012 but insisted their relationship was not close enough to warrant her declaring a potential conflict of interest when Zahalka was selected in June last year.

The committee was critical about three months worth of missing document that could explain how the photographer went from short-listed to preferred tendered.

There is also mystery as to how Zahalka could have announced to a magazine that she would be doing an assignment at Parliament a month before the department signed off on and announced her selection.

The committee interpreted the episode as once again emblematic of the dysfunction under Ms Mills' leadership. "In the committee's opinion, the commissioning of the photographs to mark the 25th anniversary of Parliament House epitomises the failings that still exist within DPS."

Ms Mills could not be contacted.