Distressing allegations have been made about the treatment of a sexual assault victim and her family on Nauru, with sources close to the investigation listing serious shortfalls by authorities.

Medical professionals have also told Lateline that 23-year-old Iranian asylum seeker Nazanin's entire family is at breaking point and suicidal.

Lateline's source says Nauruan police do not dispute that Nazanin was sexually assaulted.

In May this year she was given a pass-out from the detention centre to visit a friend.

On her way back to the centre she was grabbed by a single attacker, dragged into bushes and assaulted in a prolonged attack.

Bloodied, bruised and hysterical, Nazanin managed to escape and run down the road, attracting the attention of a passerby who called police.

It was some hours before they responded.

A friend of Nazanin's, a refugee living in the community in Nauru, was with police when she was found.

"She was not wearing any clothing, not even shoes. Just shouting," the friend said.

"She was curled up in a corner holding a stick, in a state of shock and shaking.

"When I got closer I noticed under her eyes were dark blue, bruised. There were bruises on her body."

Sources say police stopped to watch fireworks display

Sources close to the investigation said when police found Nazanin, they took her back to the police station, but not before stopping off for half an hour to watch a fireworks display.

Under the Border Force Act, anyone who has worked in an immigration processing centre can risk jail if they disclose "protected information", therefore Lateline cannot identify these sources.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 10 minutes 54 seconds 10 m Watch Ginny Stein's report into the alleged mistreatment of a sexual assault victim on Nauru

At the police station, a junior female police officer tried to question Nazanin, who was becoming increasingly distraught.

Sources said a detention centre employee stepped in to try to stop the interrogation and push for her to be taken to hospital.

Despite this, attempts to question Nazanin continued for a further three or four hours.

Meanwhile, Nazanin's family back inside the detention centre had no idea where she was and why she had not returned from visiting her friend hours earlier.

Her brother Omid told Lateline that around midnight he and his mother were told Nazanin had been assaulted.

Family told Nazanin should be moved to Brisbane

In the wake of the attack, Nazanin's health deteriorated.

She had been kept separate from her family for some time and she was not eating.

When her kidneys shut down, the family was told Nazanin should be moved to Brisbane.

Omid said they were told there was only room on the plane for his sister, but they were under the impression they would be able to join her later.

"The doctor and another team leader, both of them had a meeting with us and they told us on Sunday we will join my sister," he said.

"It was really hard, but I persuaded my mother, just lay here for two days and we will join her. So we just allowed them to send Nazanin.

"Unfortunately later we understood it was completely a trick to just taking Nazanin and her alone."

Two medical staff on Nauru have resigned over the treatment of Nazanin and her family.

Lateline has tried to contact them without success.

Family begging to be reunited

Nazanin's mother is distraught over the family's treatment and is begging the Federal Government to reunite them.

"As a mother, I cannot tolerate the suffering of my child. I don't want to live," she said.

She and Omid are able to occasionally call Nazanin, who remains in care in a Brisbane hospital, but Omid said each time was traumatic.

"She is a young girl being alone in hospital, she is scared and just always crying whenever we have a phone call," he said.

"My mother, my sister, they are dying gradually, they are dying and we are really alone here.

"All the doctors and trauma specialists and the psychologists, all of them are saying that the most important part of my sister's medical recovery is she needs her mother, she needs her family to be beside her."

Lateline has been told that police on Nauru mishandled their treatment of Nazanin. ( Torsten Blackwood: AFP )

Psychiatrist Helen Driscoll is one of Australia's leading trauma experts and has been in contact with Omid.

He gave her permission to speak about him.

"The first time I talked to him he was distressed and talking about his sister and whether there could be any assistance and he was struggling with despair," she said.

Since then, both Omid and his mother have attempted suicide.

Dr Driscoll said the family desperately needed to be together.

"One of the profound treatment needs when somebody is traumatised is to reverse that what occurred during the trauma, that is, there needs to be safety, there needs to not be isolation, there needs to be connectiveness, warmth and dignity," she said.

She fears the family is at breaking point.

"The demise of these three members of the family is not only occurring, but it's actually quite critical and they may all die," she said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 15 minutes 36 seconds 15 m Richard Marles says greater transparency is needed on Nauru amid allegations of police incompetence.

Immigration Minister Peter Dutton said as recently as this month that it was Government policy to allow family members to travel with asylum seekers receiving medical care off the island.

The Department of Immigration and Border Protection provided a statement to Lateline on Nazanin's case.

"The individual concerned has been receiving appropriate medical and mental health support and care," it said.

"The Department takes allegations of sexual assault and criminal conduct very seriously and immediately refers them to the appropriate authorities for investigation."

"The Department reviews all requests for family reunification on a case by case basis."