In March this year, she filed an appeal against her conviction.
Mr Nisbet's sister Lee-Anne Cartier, who was praised by police for her detective work in bringing Milner to justice, said she would attend the half-day appeal in Wellington.
"It's just part of the process. It's not like it can go anywhere. It's just another attempt by her to get off, and it's not going to work,'' the 44-year-old said.
Ms Cartier had been living in Australia when her brother died.
But after suspicions that Milner may have killed him, she moved back to Christchurch and started her own investigations.
She returned to the Sunshine Coast only after Milner was sentenced earlier this year.
But she has vowed to return to New Zealand in July - along with elder brother Andrew - to witness proceedings.
"I'm going to be there every time she sticks her stupid little head up to bop it back down again,'' Ms Cartier said.
If unsuccessful this time, Ms Cartier fears Milner will also appeal through the Supreme Court, and also appeal her sentence.
"To keep face, she had to appeal. She has to keep up the pretence that she's innocent.''
This weekend marks the fifth anniversary since Milner cooked Mr Nisbet his evening meal, laced with a fatal dose of sedative drugs.
Ms Cartier is frustrated that because of the initial bungled police probe, which ruled suicide, that the case is still ongoing.
"If the police had done their job to start with, then this appeal stuff would have been over two years ago, and we'd be getting our lives back together,'' she said.
"Instead, my parents are so frail and unwell now that they're not well enough to attend an appeal.
"If the trial had been three years ago, their health wouldn't have deteriorated as it has with the stress of it, and they would have some quality of life. That's what's so upsetting.''
