The daughters of Australia's richest person, Gina Rinehart, were photographed together at an intimate dinner celebrating Bianca's 40th birthday party in Perth recently.

The dinner is chronicled in the latest issue of Vogue Australia despite it reportedly being a "very private party".

"A long and public court battle won, Bianca is in a happy place and wanted her people around her," the party report read.

Bianca, who replaced her mother as trustee of the estimated $5 billion Hope Margaret Hancock Trust back in 2015, celebrated her "milestone birthday" at the glass-roofed restaurant at Como The Treasury - an establishment voted second-best hotel in the world by leading travel publisher, Conde Nast Traveler, last year.

For years Bianca and Ginia were on different sides of the bitter war over the family's multibillion-dollar trust.

Ginia sided with her mother, while Bianca and brother John Hancock, claimed documents and accounts relating to the trust established by their grandfather, Lang Hancock, had been withheld from them by Gina. They also claimed Gina had failed to declare up to $500 million in dividends from the family's flagship company, Hancock Prospecting.

The 3½-year family rift, that played out in the NSW Supreme Court, initially pitted Ginia, 30, against Bianca.

In the early proceedings in 2013, Ginia requested Bianca's medical records relating to any psychological issues become part of an investigation into whether Bianca would be an appropriate person to usurp Gina as manager of the trust.

Bianca was diagnosed with an eating disorder at 18 and was treated at a London clinic, which was paid for by Gina. She was also treated for depression, not relating to an eating disorder, in 2000 and 2003.

At the time Bianca spoke out in defence of Ginia's actions and used the opportunity to advocate for mental health.

"My whole family knows I had an eating disorder in my late teens. I love my sister and bear no animus towards her for this approach and I'm addressing it as I strongly feel that nobody should be ashamed to seek help for any mental illness and have the support of their loved ones in so doing," Bianca said in 2013.

Earlier this year Bianca was granted permission by the NSW Supreme Court to sue Gina for alleged breaches of duties as trustee of a family trust.

While "adopted family" and friends, including Olympic swimming champion Ian Thorpe and Rio Tinto chief executive Chris Salisbury, were present at Bianca's party, brother John was unable to attend.

"My wife and I were invited. We really wanted to go but my three young children had school in the northern hemisphere and the logistics of getting to Perth were too difficult at that time," he told Fairfax Media.

"[It's] good if Ginia did attend. Perhaps her eyes are finally being opened regarding the unsupportable misconduct of my mother that caused the ongoing litigation."

Foreign Minister Julie Bishop and her partner David Panton were also in attendance.

"To our deputy leader and Minister for Foreign Affairs, Julie, you are simply amazing and an incredible role model for all us girls trying to make a difference in the world," Bianca said at the party.

Founding member of Sneaky Sound System, Daimon Downey, was recruited for the evening as DJ who "turned the dinner party into a dance party under the stars into the early hours".

Hancock Prospecting has been contacted for comment.