Fatma Omari successfully overturned the will of her late mother in 2012 after launching a bitter and protracted legal battle against her brothers, Mohammed and Mustapha Omari, in the ACT Supreme Court.
As one of five daughters, Fatma Omari initially received just a half share of the estate according to the will, while her three brothers received a full share each.
She argued the will had been invalid as their Turkish-born mother, Mariem Omari, had been suffering dementia and hadn't understood what she had been doing when she signed the document in the presence of her two sons in January 2002.
Earlier that year, the brothers had been appointed their mother's guardians, citing medical reports that showed Mrs Omari had "severe cognitive impairment".
Mariem Omari, who was illiterate, signed the will with a thumb print after it was explained to her in her second language of Arabic.
In a decision handed down in 2012, then Master David Harper said he believed the brothers arranged for their mother to execute the will knowing she didn't understand what she was doing or what the effect of the will would be.
He accepted the brothers generally believed it was their mother's duty, under Islamic inheritance law, to leave one full share to her sons for every half share left to her daughters and that she would have made her will in line with those principles if she had drawn it up earlier.
Master Harper believed the brothers thought they were doing the right thing in arranging for their mother to sign the will and said he didn't think either acted out of greed.
The court ruled Mrs Omari died intestate, saying the document was void because the brothers knew their mother didn't know what she was doing and was in no mental condition to sign it.
Her will was handed to the ACT Public Trustee to execute.
The case returned to the ACT Court of Appeal this month after the brothers appealed Master Harper's decision to refuse an application for their court costs in the matter to be paid out of their mother's estate.
The pair argued they honestly believed their mother understood the nature of the will she signed, and that, as a devout Muslim, she would have ensured any will she had drawn up followed Islamic principles.
In a decision published on Monday, the full bench of the ACT Court of Appeal upheld the Master's finding that the brothers court costs shouldn't be paid out of the estate.
"The belief of the [brothers] that they were implementing their mother's wishes as a Muslim consistent with Muslim rules of inheritance did not alter the fact of the appellants' awareness of their mother's dementia and consequential lack of testamentary capacity," it said.
It found the brothers' arguments that the will should be distributed in line with Islamic law, and the fact their sister should comply with the will because she took part in Islamic burial rites for her mother, were irrelevant.
That was because the court's previous decision had been solely about their mother's capacity to make a will, the decision said.
The court dismissed the appeal, ordering the brothers pay Ms Omari's court costs. It said a $701 filing fee should be paid from the estate.