Mining magnate Gina Rinehart's estranged daughter has admitted claims she made about her mother withholding access to a deed were not true but says "it wasn't a lie I was making intentionally".
Bianca Rinehart took the stand in the Federal Court on Monday in the latest legal stoush to embroil the family.
She has joined forces with her brother John Hancock in legal proceedings against their mother and Hancock Prospecting, in which they are seeking profits from the company.
In a separate case from the trust fund battle before the Supreme Court, they are saying in the Federal Court their grandfather Lang Hancock also set up the Hancock Family Memorial Foundation (HFMF) for them in 1988.
They say the 1988 agreement meant that upon his death their mother would own 51 per cent of Hancock Prospecting while his grandchildren would have a 49 per cent stake in the company and own 100 per cent of HFMF.
When Mr Hancock died in 1992, they said HFMF had a 33 per cent share in Hancock Prospecting and held the Hope Down tenement, Mulga Down tenement and was pursuing the exploration licence for Roy Hill.
But now Bianca and John Hancock's barrister Christopher Withers told the Federal Court, "all these assets held on trust for the children have been taken away from HFMF".
The children's share in the company is now down to 24 per cent while their mother's has grown to 76 per cent, he said.
"It happened because Mrs Rinehart controlled everything ... She never did anything to ensure their assets were protected," Mr Withers said.
Bianca told the court: "I didn't know anything about the HFMF trust. I didn't know it existed."
She claimed her mother had also withheld information on a inter-creditor deed, which dealt with how dividends were paid.
But her mother's barrister Bruce McClintock SC repeatedly took her to a number of emails sent to her in 2006 about the deed.
"The statement ... that you did not have access to the inter-creditor deed is not true is it?" Mr McClintock asked.
She agreed, but said: "It wasn't a lie I was making intentionally."
"It was almost 10 years ago now so my recollections may not be crystal clear."
She said there were "specific instructions" not to allow her to take documents out of the office.
But she conceded that from around 2004 she started taking documents regarding the family trust in a bid to get to the truth of the dispute between her brother and mother.
She said she also didn't realise the true ramifications of signing the Hope Downs Deed in 2007, adding that she now believes it was to "silence us".
"I was taking for granted what my mother was presenting to us was the truth as most children do," she said.
Speaking outside court, Bianca said it was a "very hard time for us all".
The hearing continues.
