An inquest into the death in custody of an Indigenous woman heard her health was declining in the month prior to being found in a critical condition by her sister at Dame Phyllis Frost Centre.

The hearing into the death of Yamatji, Noongar, Wongi and Pitjantjatjara woman Heather Calgaret in Naarm was told in the month leading up to her death she had expressed wanting to find and take drugs.

Ms Calgaret's mental health was declining as she was told her parole application had been denied, and she was suffering from anxiety about her partner - who had just been released from prison - relapsing.

A corrections officer said Ms Calgaret was holding on to hope of seeing her children and was worried they would become wards of the state.

The hearing on Monday heard Ms Calgaret arrived in prison six months pregnant, having been found guilty of armed robbery.

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), which drastically impacted her mental health.

"My kids need me before it's too late," she told a corrections officer in the lead-up to her parole application, which was denied due to a lack of suitable accommodation a month before her death.

Ms Calgaret died at Sunshine Hospital in November 2021.

An autopsy found she 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.

The inquest over the next month is examining state's parole system for the first time since the laws were toughened, Ms Calgaret's treatment in prison, and if the 8mg of Buprenorphine (Suboxone) she received the day prior to being found unconscious was a factor in her death.

Tammy Innes, a former inmate appearing on Tuesday, said Ms Calgaret was a popular inmate, and asked why she would be given Suboxone, given she wasn't a substantial opioid user.

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

The hearing has heard Ms Calgaret had dental surgery on the same day she collapsed, as well as being given her first round of Suboxone.

Ms Innes said she'd witnessed Ms Calgaret use small doses of Suboxone - unprescribed - by placing oral strips in her mouth during the month before her first injection.

"I think she [Ms Calgaret] liked the effects of it," Ms Innes said. "She wanted to be drug free and there for her kids."

She told the court Ms Calgaret had expressed a belief the use of Suboxone would stop her relapsing when she was eventually paroled.

Earlier, a corrections officer said staff had raised concerns about Ms Calgaret in the lead-up to her death, noting her revelation of a desire to take drugs again had sparked a referral for urgent care.

Noting Ms Calgaret had expressed to her she could "find drugs whenever she wanted to," the officer - who cannot be named - said: "She'd never been that blunt with me before, so I was very concerned about it."

The officer said her death had a significant impact on others in the unit.

"They were devastated. Heather was such a big personality and so well liked, and probably a bit of a leader in her group," she said.

On her appearance after dental surgery, the officer said Ms Calgaret looked exhausted, and had reported not feeling well that afternoon before she collapsed.

"...but not sick enough for me to call a code," she said.

The inquest before Coroner Sarah Gebert continues Wednesday.