A 16-year-old-girl who died of a drug overdose while in Victorian state care had previously been infected with hepatitis C by a recently released prisoner, an inquest has been told.

Key points: The inquest is examining the actions of Maria's carers in the lead up to her death

The inquest is examining the actions of Maria's carers in the lead up to her death The decision not to call an ambulance when Maria was found drug affected has been scrutinised

The decision not to call an ambulance when Maria was found drug affected has been scrutinised The case is shining a spotlight on how high-risk children are treated in state care

The prisoner was allegedly allowed to send letters sexually grooming Maria Liordos to her residential care unit, and sexually assaulted and used drugs with her after he was released.

Maria was found dead in a house in Melbourne's western suburbs in 2013 in the early hours of the morning after allegedly using drugs earlier at the residential care unit, which was operated by the Salvation Army's Westcare agency.

Much of the evidence already heard by coroner Audrey Jamieson revolves around actions by Westcare staff on the night of Maria's death, and whether or not an ambulance should have been called given her drug-affected state.

The actions of Maria's high-risk case manager, who was telephoned by unit staff that night, have also come under significant scrutiny.

The inquest also heard that Maria was allegedly sexually assaulted by a carer at her unit, and that she felt that after reporting the alleged assault, she was ostracised by other staff at the unit.

Spotlight on treatment of Victoria's most vulnerable children

The case is shining a spotlight on Victoria's residential care system, which is operated largely by outside agencies under contract to the Department of Health and Human Services.

The system houses hundreds of the state's most vulnerable children, many of whom have suffered serious sexual and physical abuse and struggle with substance abuse and mental health problems.

The children live in houses scattered across the state, either alone with a carer, or with a number of other children.

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The ABC revealed in 2014 that children in the system, aged predominantly between eight and 17-years-old, were being targeted by groups of paedophiles for sexual exploitation in return for money, drugs, alcohol and consumer goods.

A spokesman for the department described Maria's death as a "tragedy", and said the department was working with the Coroner's Court to bring all the circumstances around Maria's death to light.

The State Government has introduced a number of measures to try and improve the care provided to the children in the units, including spot audits of the units, mandatory qualifications for carers and mandatory "stand up" staff for the units at night.

The night before Maria died

In the case of Maria Liordos — a child deemed at "high risk" due to a history of sexual abuse, substance abuse and mental health problems — neither of the carers on duty at her unit the night she died had any qualifications related to caring for high-risk children, and both had only been working in the field for a short period of time.

Westcare claims it has made significant changes to the way it cares for children deemed at high risk since Maria's death.

The inquest heard that on the night before she died, Maria returned to her unit with her girlfriend. The carer on duty, Alannah O'Brien, gave evidence that Maria was already drug-affected, and that after going to the toilet at the unit, she appeared to be even more under the influence.

Ms O'Brien described Maria as "severely" drug-affected, and said she was aggressive, having trouble walking and slurring her speech.

A later search of the bins in the toilet discovered drug paraphernalia, including syringe wrappers.

Maria and her girlfriend then left the unit and went to the house of a 26-year-old male acquaintance, where Maria's girlfriend discovered her lifeless the next morning.

Should an ambulance have been called?

A high-risk drug crisis plan for Maria stated that staff should call an ambulance when she was deemed "at risk", but Ms O'Brien said the time between Maria emerging from the toilet and leaving the unit was too short for her to have called an ambulance.

A second worker, Kym Studley, then arrived for duty on the night in question and had a conversation with Ms O'Brien about Maria.

While Ms O'Brien filled out an incident report about Maria, Ms Studley phoned Maria's Westcare case manager, Michelle Hines, and told her what had happened.

Ms Hines gave evidence that Ms Studley had said Maria's eyes "were rolling back in her head".

Ms Hines told the inquest she would have expected Ms O'Brien or Ms Studley to call an ambulance if they believed Maria was at risk, but both carers said they believed it was Ms Hines' responsibility.

"To place that responsibility on somebody I think is quite unfair," Ms Hines said in response to questions from counsel assisting the coroner, Tracey Ramsey.

"If you accept a position of employment ... you undertake your job responsibilities and you perform ... the tasks that are required of you."

Allegations Maria was deliberately infected with hep C

Although the inquest is concerned with the events directly leading to Maria's death, Christine Willshire, a lawyer for Maria's mother, raised the allegation that an adult male prisoner was able to "groom" Maria for sex through letters sent to her residential care unit.

Ms Willshire asked Ms Hines whether she was aware of allegations that when the prisoner was released, he met with Maria, sexually assaulted her and deliberately infected her with hepatitis C through a shared needle, telling her "now that I've injected you ... we can be together forever".

Ms Hines said she was aware of the allegations, and that she believed the letters had been referred to a senior manager at the department, but that she did not recall whether police had been told about them.

A psychologist treating Maria, Alice Barnacle, said she had discussed Maria's alleged sexual assault at the hands of a Westcare worker with her, and had worked to help Maria understand the alleged assault was not her fault.

She said Maria felt she was being treated differently by other staff after reporting the incident, and that "they didn't like her anymore".

The Westcare staff also gave evidence that they could be on hold to the department's after hours number for up to three hours, although a lawyer for the department disputed this.

The inquest continues.