The inquest into the death of Heather Calgaret, who died in Victoria's Sunshine Hospital while in custody, began on Monday.

Since the Royal Commission into Aboriginal Deaths in Custody brought down its recommendations in 1991, more than 550 Aboriginal people have died in custody.

Outside the Coroner Court in Naarm, Ms Calgaret's brother, James "Chum' Smith, read a statement, describing his sister as the "rock of our family".

"We were heartbroken by her death," he said.

"Life is precious, Heather's life is precious. It shouldn't have been taken away from her."

Ms Calgaret, a Yamatji, Noongar, Wongi and Pitjantjatjara woman, passed away in November 2021, having been found in a critical condition by her sister Suzzane at Dame Phyllis Frost Centre Prison.

The mother-of-four died after being denied parole, and the inquest will examine the state's parole system for the first time since the laws were toughened, as well as Ms Calgaret's treatment in prison, and if the 8mg of Buprenorphine she received the day prior to being found unconscious was a factor in her death.

Buprenorphine, or Buvidal, is often given to people who are experiencing opioid dependency or withdrawals.

An autopsy found that Ms Calgaret suffered brain damage due to oxygen deprivation, as well as an enlarged heart and other signs of cardiac disease, including a narrowing of the coronary arteries.

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Ms Calgaret was only months from completing her sentence when she died and was living in the prison's reintegration unit.

She had been denied parole due to a lack of suitable accommodation a month before her death.

Counsel assisting the coroner, Sharon Lacey, said Ms Calgaret was six months pregnant when she arrived at Dame Phyllis Frost for armed robbery, and was classified as a violent offender.

Ms Lacey said Ms Calgaret reported "no previous medical condition" and appeared "well" to the medical officer who examined her.

She applied to have her newborn child remain with her in the Mother Baby Unit, however this was denied, citing concerns raised by the Child Protection division of the Department of Families, Fairness and Housing (Child Protection).

Five days before the birth, Ms Calgaret was told of this.

Over the coming months, she began to suffer from depression, with the forensic psychologist she spoke to in prison observing Ms Calgaret "spoke of feeling overwhelmed in custody" and reported suicidal thoughts, particularly following the birth of her youngest child and their subsequent removal from her care.

Aboriginal Wellbeing Officer Aunty Lynne Killeen said the decision left Ms Calgaret "extremely traumatised" and not coping well.

By the time of her death, she had been diagnosed with several health conditions, including diabetes, heart problems, depression, and obesity, and had been prescribed a number of different medications, including anti-depressant and anti-psychotics.

Ms Lacey said the inquest would look to resolve if the dose of buprenorphine, or Ms Calgaret's health conditions played a role in her death.

The inquest will hear from witnesses - including prison guards and former prisoners - as well as experts in mental health, toxicologists, cardiologists, and cultural carers.

The coronial brief includes more than 4000 pages of documents.

The inquest is set to run for four weeks.

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