Bevan Chuang is confident Len Brown will be cleared by a spending inquiry in the wake of their extra-marital affair, saying he paid for everything out of his own pocket.
However, she believed that some of the rooms he booked for the pair were offered free of charge by hotel managers.
Auckland Council chief executive Doug McKay yesterday announced an inquiry into Mr Brown's spending in the wake of the sex scandal.
Ms Chuang said she met Mr Brown three times at the Langham, SkyCity Grand and Hilton hotels for sex after collecting the keys to the rooms from reception at the Town Hall.
A spokeswoman for the Hilton said the hotel would not give complimentary rooms to Mr Brown, while spokeswomen for SkyCity and the Langham hotels would not comment on guests for privacy reasons.
A mayoral spokesman said any expenses Mr Brown incurred relating to the relationship were paid out of his own pocket, including private accommodation.
The 32-year-old former mistress said: "He sometimes takes some time off and goes to hotel rooms, and quite a few times managers would tell him 'it's fine, it's on us. We can organise somewhere private for you'.
"He often feels uncomfortable and wanted to go down and pay but usually the manager would [insist] 'no no, it's on us'."
The rooms also came with antipasto food platters and nuts, she said.
Ms Chuang believed the rooms were offered free to Mr Brown so that he could "talk about" and "recommend it" for council patronage.
Mr Brown would check-in at the hotel himself and then arrange for a spare room key to be delivered back to the council in an envelope addressed to Ms Chuang.
Ms Chuang, who also speaks Cantonese and Mandarin, claimed Mr Brown used the mayoral car and driver to pick up and drop her off on two occasions when he took her to council dinners as his interpreter.
During their two-year-affair, Mr Brown had bought her several gifts including a bottle of Chloe perfume, a black bra and g-string and a bottle of sunblock.
He also bought her mother a Rugby World Cup All Blacks DVD.
Ms Chuang, who has said that she regretted going public about the affair, is backing Mr Brown in the inquiry and believed everything he spent on her was "from his pocket" and "above board".
The mayoral spokesman said Mr Brown was not commenting on individual allegations relating to the relationship, but stressed "any expenses he incurred, he paid for out of his own pocket. That includes private accommodation".
"The mayor's car is for both private and public use, just like most company car arrangements. He often gives lifts to colleagues, friends and associates to and from meetings, functions and engagements in a reasonable way."
In other developments yesterday, it emerged that Ms Chuang has a criminal conviction for logging into the email of the former head of the Auckland Museum.
She was charged with unlawfully accessing a computer system, pleaded guilty and fined $1000.
Mr Brown also confirmed he provided a reference for Ms Chuang to help her get a job at the council-run art gallery in July 2011 - two months after Ms Chuang says the affair began.
The mayor's office said the office was contacted by email by the Auckland Art Gallery on July 4, 2011 and asked to provide a reference in relation to the application.
"On July 5, at the mayor's request, the mayor's diary manager responded by email to say that the mayor highly recommended Bevan.
"The diary manager also asked in the email that the person call her to discuss. As the staff member left some time ago we're not sure whether the call was returned and whether she discussed the reference further," the office said.
A document carried by a Government minister yesterday appeared to anticipate the resignation of Auckland Mayor Len Brown.
Local Government Minister Chris Tremain was spotted holding a page with the headline "Lines for Mayors resignation" in Parliament
A spokeswoman said that the document was prepared for the minister in case he was asked questions about the mayor during Question Time.
Mr Tremain said that Mr Brown's future was not his responsibility and he was only concerned about legislation which related to local government.
The document listed the situations in which a mayor could be removed from office: "For example if they are absent from four consecutive council meetings without leave, are convicted of a serious offence, are ruled incapable of holding office by a judge, or are disqualified from being an elector under the Electoral Act.".
It also listed the process if a mayor was to stand down, saying that a byelection was required to fill a vacancy.
Yesterday, the mayor's office said Mr Brown intended to continue in the job.
• Chloe perfume
• Black bra and g-string
• All Blacks DVD