Gina Rinehart’s daughter Bianca says appointing her trustee of the multibillion dollar family trust is “a significant step towards restoring family harmony”.

A NSW Supreme Court judge on Thursday named the iron ore magnate’s eldest daughter as the best person to control the trust, estimated to be worth up to $5 billion.

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“I am pleased that as a result of this judgment, the trust he set up will now be able to be managed in the best interests of its beneficiaries – my sisters, my brother and myself,” Bianca said in a statement, referring to her grandfather Lang Hancock.

The statement followed John Hancock predicting his mother will appeal Thursday’s Supreme Court decision.

He says he can’t imagine his mother accepting the decision to hand control of the fund to Bianca after a bitter three-year legal dispute.

In a damning judgment, Justice Paul Brereton said Mrs Rinehart had used tactics bordering on intimidation in her battle with her two elder children over the fortune.

He said she’d gone to “extraordinary lengths” and exerted enormous pressure to maintain control of the trust, including enlisting the help of federal cabinet minister Barnaby Joyce.

Mr Hancock said he was stunned by Mr Joyce’s intervention in a family dispute, and the federal agriculture minister has questions to answer.

He said Mr Joyce was “manipulated” into emailing his younger sister Hope Welker, urging her to abandon legal action against their mother.

“Coming from his government email, I just think it’s extraordinary. This character sits three chairs down from our prime minister,” Mr Hancock has told ABC radio.

“It’s nothing short of dangerous … When you see the findings on my mother’s conduct, questions need to be raised about why he got involved in this.”

Mr Hancock said an appeal by his mother was all but certain, given how hard she’d fought every other aspect of the legal battle.

“Every single decision along the way she’s appealed all the way to the High Court. So I can’t see this being any different,” he said.

Lawyer Alan Camp, who has worked with the Rinehart family for more than 40 years, and is now a confidant of John Hancock and Bianca Rinehart said he believed the family would ultimately reconcile.

“They are all very robust individuals and once resolved, everything will be resolved,” he told ABC television.

“It’ll take time but John and Bianca are very understanding people. They know what’s got to be done but they also know all the emotions that’s involved and they have considerable care towards their mother.”

AAP has sought comment from Mrs Rinehart about any appeal.