The award of $25 million to the youngest daughter of the late Perth mining billionaire Michael Wright has been slashed to $6 million after his estate appealed.

Olivia Mead, who was born from Mr Wright's relationship with Elizabeth Anne Mead after he divorced three wives, was aged 19 in 2015 when Master Craig Sanderson of the Supreme Court of Western Australia ruled her bequest should be increased more than eightfold.

The estate argued in the WA Court of Appeal that the $3 million Ms Mead had originally inherited was adequate for her proper maintenance.

Olivia Mead (pictured) will recieve $6 million after father, Michael Wright's estate appealed

The award of $25 million to late Perth mining billionaire Mr Wright's (pictured) youngest daughter was slashed

During the appeal, the estate took aim at the now 22-year-old's extravagant wishlist, which was submitted to estimate her future needs

On Wednesday, the full bench of judges unanimously set aside Master Sanderson's orders, instead awarding the 22-year-old $6.14 million.

Ms Mead's older half-sisters, Leonie Baldock and Alexandra Burt, were left most of their father's estate - about $400 million each.

During the appeal, the estate took aim at the now 22-year-old's extravagant wishlist, which was submitted to estimate her future needs.

Her list of demands included a diamond-encrusted bass guitar worth $250,000, a house almost five times the Perth average price, $10,000 a year to spend on fashion accessories, and a $US1.2 million limited edition, crystal-studded Kuhn Bosendorfer grand piano.

She also sought an Audi, money for the upkeep of four children she plans to have - each two years apart - and thousands of dollars a year to care for four pets including an axolotl or 'Mexican walking fish'.

Jane Needham, representing estate executor David Lemon, cited Ms Mead's call for 20 pairs of $300 shoes every year for the next 75 years and Pilates lessons until she was aged 97, which Justice Michael Buss labelled 'just silly', saying what might be needed was a reasonable house and income.

On Wednesday, the full bench of judges unanimously set aside Master Sanderson's orders, instead awarding the 22-year-old (pictured) $6.14 million

Ms Mead also sought an Audi, money for the upkeep of four children she plans to have - each two years apart

The 22-year-old also sought thousands of dollars a year off her father (pictured) to care for four pets including an axolotl or 'Mexican walking fish'

Ms Mead's lawyer Lindsay Ellison argued the court could take everything into account when assessing what a daughter from a wealthy family might need for the rest of her life, saying the $25 million award was large but 'minimal compared to the size of the estate'.

There were also no competing claimants, he said, and the court could 'go that extra bit further, and add some cheese and jam' rather than just the essentials of life.

Ms Mead was not present in court when the judgment was handed down.

Ms Mead's older half-sisters, Leonie Baldock and Alexandra Burt, were left most of their father's estate - about $400 million each.

Ms Mead, who was born from Mr Wright's relationship with Elizabeth Anne Mead (pictured) after he divorced three wives

Ms Mead's older half-sisters, Leonie Baldock and Alexandra Burt, were left most of their father's estate - about $400 million each

Ms Mead's share was only going to be available when she reached age 30 and clauses in the will included limiting her religious affiliation, which meant she could have ended up with nothing.

Jane Needham, representing estate executor David Lemon, told the full bench of the WA Court of Appeal on Thursday that $3 million was adequate for the proper maintenance of Ms Mead, who compiled a lavish wishlist to estimate her future requirements.

It included a $US1.2 million crystal-studded grand piano, a diamond-encrusted bass guitar, upkeep for her pet axolotl and provision for four children that she plans to have, and originally amounted to $20 million but was revised down to about $12.5 million.

Ms Mead's share was only going to be available when she reached age 30 and clauses in the will included limiting her religious affiliation

Master Sanderson said Ms Mead had simply let her imagination run wild the same way most teens would if asked to outline such needs, was not 'a gold digger' and awarded her $5 million more than she had initially asked for.

But Ms Needham said Master Sanderson had in effect regarded the size of the estate as trumping any other factor he needed to consider and he erred in regarding his discretion unfettered.

She said it was wrong to award Ms Mead twice as much as what she ultimately sought after considering 'some quite extraordinary items' - even in the revised wishlist - without accounting for her or her partner's future income.

Ms Needham cited Ms Mead's call for 20 pairs of $300 shoes every year for the next 75 years and Pilates lessons until she is aged 97.

Ms Needham cited Ms Mead's call for 20 pairs of $300 shoes every year for the next 75 years and Pilates lessons until she is aged 97 (pictured is Olivia with Mr Wright)

Justice Michael Buss said he made no criticism of Ms Mead, but such items were 'just silly'.

He asked how the judges would evaluate what was proper in the circumstances, saying a reasonable house and income might be what was needed.

Ms Needham also said it wasn't appropriate to make the estate provide for Ms Mead's planned four children.

But the 21-year-old's lawyer Lindsay Ellison said there was nothing that couldn't be taken into account when assessing what a daughter from a wealthy family might need for the rest of her life.

'It is a large result but it's minimal compared to the size of the estate,' Mr Ellison said.

There were also no competing claimants, he said, and the court could 'go that extra bit further, and add some cheese and jam' rather than just the essentials of life.