The Narre Warren property in Melbourne's southeast is central to Amorosi's legal case against her mother Joyleen Robinson, which has gone to trial in the Victorian Supreme Court.
Amorosi claims the $650,000 used to purchase the home in 2001 came from a trust account set up to receive all of her earnings as a singer-songwriter.
She is seeking full ownership of the property, which currently has her and her mother listed as joint-owners.
But Mrs Robinson claims Amorosi agreed to hand over full ownership of the Narre Warren home if she paid $650,000 when asked.
In his closing arguments on Wednesday, Amorosi's barrister Joel Fetter told the court the agreement never happened and it was merely Mrs Robinson's invention.
Mr Fetter said the first time the agreement was mentioned was in a 2015 letter, but even that note did not reference when the pact was made.
Mrs Robinson's husband Peter was also not aware of any agreement when he was questioned during his evidence, Mr Fetter said.
Justice Steven Moore also found it "very strange" that Mr Robinson wouldn't have known about an agreement made between his wife and stepdaughter.
"It's very unusual a wife wouldn't tell a husband," he told the court.
But Mrs Robinson's barrister Daniel Harrison said Mr Robinson himself said he left all financial matters to his wife.
Mr Harrison maintained there was an agreement between Amorosi and her mother, and his client merely did not document such matters.
He also accused Amorosi of giving unreliable evidence to the court, saying she repeatedly couldn't recall key dates.
But Mr Fetter said only Amorosi's version could be considered the truth as she gave convincing evidence of the discussions she had with her mother.
Justice Moore on Wednesday reserved his judgment, which will be handed down at a later date.
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