Bianca Rinehart, he eldest daughter of Australia's richest person, Gina Rinehart, insisted to the court on Tuesday that younger half-sister Hope Welker is on her side in their family's legal battle for control of the $5 billion trust.

Hope initially joined siblings Bianca and John Hancock in filing a lawsuit to have their mum removed as trustee of the family trust, but Hope later withdrew from the case after she agreed to a $45 million settlement with her mother.

Bianca said she does not begrudge Hope's decision, saying, "Hope had gone through a divorce, this litigation has taken a toll on all of us ... She was pretty much at her wits' end."

Just before Hope accepted Gina's offer of settlement, Hope wrote John an email in February 2013, stating, "All I feel is pain and anxiety. You are kicking me in the stomach but I'm already on the floor. Nothing left to take."

Bianca stressed that their relationship has never been stronger and she is sure of Hope's full support.

In seeking to replace her mum as trustee, Bianca said she is qualified because she had served as director and employee of the family-owned Hancock Prospecting before she had a falling out with her mother. She also warned that the joint venture between Hancock and Rio Tinto to develop the Hope Downs giant ore mine could be placed at risk.

Bianca likewise said she disagreed with the language used by her brother in describing their youngest sibling Ginia, who has sided with their mum from the start of the conflict, but said he merely wants to protect the trust funds from being handled by someone who is not a direct lineal descendant of their grandfather Lang Hancock who established the trust.

Read: Rinehart Family Feud Turns for the Worse as John Calls Sister Ginia Moron, Oxygen Thief & Intellectially Disabled

The name-calling stems from Ginia supporting mum's recommendation to appoint an independent trustee and not Bianca.

But even Bianca admitted she and John also had a falling out after she told Gina in 2004 that she was concerned about John's "reckless bite the hand that feeds your approach." The 37-year-old Bianca said it was not a personal attack on her brother but a reference to his drinking and gambling problems then which was damaging.

"Everyone drinks from time to time I believe that it is no longer an issue ... I may have believed that at the time," she said.

Bianca also admitted calling John an idiot in the past, saying, "I may have, I do not always agree with everything he does."

Christopher Withers, the lawyer of Bianca, had accused the billionaire miner of subjecting his client to threats and intimidation since she and her two siblings initiated the legal action against their mum.

Withers said, "Anybody who can stand up to that kind of conduct ... has got the strength of character to do this job," to justify the two siblings' push for Bianca to be appointed trustee.