A Sydney high school teacher who was allegedly involved in a scam with her sister and their partners to secure $1.3 million in contracts from the state government has been accused of lying to the corruption watchdog.

Fayrouz Abou Chacra is being investigated by the Independent Commission Against Corruption over claims her husband's companies were awarded lucrative contracts to upgrade courthouses across the state while her sister was working in the NSW justice department.

The ICAC has heard the contracts were grossly inflated and in some cases the companies were paid for doing no work.

Ms Abou Chacra has given evidence she was "surprised" to learn her sister was employed by the department when she attended a meeting on behalf of one of the companies in 2013.

The contracts were awarded by Anthony Andjic, who was in charge of capital works in the department and was in a relationship with Ms Abou Chacra's sister, Fatima Hammoud. The pair married this year.

The inquiry has heard it was a "well-known secret" in the department that the pair were in a relationship but no conflict of interest disclosure was made.

One of Mr Andjic's former supervisors has said he gave him "the opportunity to come clean" about the relationship and "he flat out refused it and said ... he's sick of all the rumours and innuendos".

Ms Abou Chacra, who works as a PE teacher at a public high school in southern Sydney, was the "public face" of one of the companies, Saff Projects, in its dealings with the justice department.

She referred to herself as "Fay Rouze" for these purposes but denied suggestions by counsel assisting the inquiry, Grant Brady, that she was trying to "avoid using the last name Hammoud because it'd strike a chord with the fact that [her] sister Fatima Hammoud was working at the department".

Ms Abou Chacra was warned about giving false or misleading evidence to the commission on Tuesday as she repeatedly claimed to have no recollection of events.

"Are you just making this up as you go along?" Commissioner Megan Latham asked.

"No,  I'm telling you the best from my memory back then," Ms Abou Chacra replied.

She agreed that bills for court refurbishment works, which were submitted by a company owned by her now husband Shadi Abou Chacra, were "dishonest" but bristled at suggestions they were fraudulent.

"The bills were a fraud, weren't they?" Mr Brady said.

"I'm not going to agree with that statement," Ms Abou Chacra said.

The inquiry has heard Mr Andjic awarded 17 projects to Mr Abou Chacra's companies, Triton Group and Saff Projects, including for projects at a building in Spring Street in Sydney and courthouses in Camden, Picton and Cessnock.

None of the contracts should have been awarded without a tender.

In some cases, the value of the contracts was inflated by hundreds of thousands of dollars. Mr Brady said in his opening address that the companies "did nothing" to make almost $100,000 in Cowra, East Maitland and Gunnedah.

The companies' total profit was almost $1 million.

The inquiry continues.