While clearing out her mum's wardrobe, Elly Tyquin found a music box she was meant to get for her 21st birthday, and her heart broke all over again.

The discovery came after Melbourne fitness trainer Rachel Tyquin was killed by her neighbour during an early morning walk at Sunbury in April 2016.

The 44-year-old, who was engaged to be married, was stabbed 19 times with a kitchen knife and died on the nature strip in her active wear. Eva Whitecross, 55, inflicted the wounds but she was found not guilty of murder in August because of mental impairment.

The stabbing followed years of verbal abuse from Whitecross aimed at Ms Tyquin over a perceived parking dispute.

Elly was forced to grow up fast after the death, speaking to detectives, funeral organisers and counsellors. She eventually gathered the strength to go through her mother's belongings. She found old letters, photos, clothes - and her 21st birthday gift.

'My birthday present, half finished, was hidden in her wardrobe. It included a music box on which she had written 'Happy 21st, beautiful daughter. Love Mum,' Elly said.

'Finding that gift broke me. The song it played, I couldn't listen to it for months.'

While clearing out her mum's wardrobe, Elly Tyquin (pictured right with aunt Colleen) found a music box she was meant to get for her 21st birthday, and her heart broke all over again

Melbourne fitness trainer Rachel Tyquin was killed by her neighbour during an early morning walk at Sunbury in April 2016

The 44-year-old, who was engaged to be married, was stabbed 19 times with a kitchen knife and died on the nature strip in her active wear

Whitecross was suffering from a delusional disorder, the Victorian Supreme Court found.

Justice Jane Dixon on Wednesday ordered her to live at a psychiatric facility indefinitely, with a 25-year nominal term.

But Elly, 22, hopes her mum's killer will never be released. She's lost her best friend, confidante and role model.

'I lost a part of me, the day mum died,' Elly told the court in a statement.

'She was a strong, kind-hearted, caring, beautiful woman, and I was proud to call her my mum.'

But Elly, 22, hopes her mum's killer will never be released. She's lost her best friend, confidante and role model

'I lost a part of me, the day mum died,' Elly told the court in a statement. 'She was a strong, kind-hearted, caring, beautiful woman, and I was proud to call her my mum'

'It is very apparent that Rachel Tyquin was a vivacious and inspiring woman in the prime of her life,' Justice Dixon said. 'She was held in very high regard by those who knew her'

On the day of the attack both women were walking their dogs when their paths crossed about 6am. After the stabbing, Whitecross walked home, had a shower and made a cup of coffee before driving to the police station

The court was told Ms Tyquin was a busy fitness trainer who planned to visit Europe with her daughter.

'It is very apparent that Rachel Tyquin was a vivacious and inspiring woman in the prime of her life,' Justice Dixon said. 'She was held in very high regard by those who knew her.'

On the day of the attack both women were walking their dogs when their paths crossed about 6am.

After the stabbing, Whitecross walked home, had a shower and made a cup of coffee before driving to the police station.

Justice Dixon said she had hurled 'vile' abuse at the victim for seven years as her delusions grew, calling her a 'moll' and a 'wh*re'.

Whitecross will undergo psychotherapy while she lives in supervised custody at Thomas Embling Hospital.