A young Iranian asylum seeker, who could return to Nauru with his family, is worried his mother will die in immigration detention.

Key points: 70yo Iranian woman faces prospect of returning to Nauru detention centre

70yo Iranian woman faces prospect of returning to Nauru detention centre Son, lawyer fear for her mental state

Son, lawyer fear for her mental state Son says sister attempted suicide at Nauru

Son says sister attempted suicide at Nauru Immigration Department says cases reviewed on individual basis

His family is one of hundreds at Darwin's Wickham Point detention centre that face the prospect of being deported to a country they fear, after the High Court on Wednesday ruled offshore detention legal.

The man, who cannot be named for legal reasons, said the news broke his 70-year-old mother, who is the oldest woman in detention.

"We had hope before. People told us, 'don't worry, you have to wait to High Court' and when she heard on TV and news we lost High Court and then she just [started] crying and hitting her head," he said.

"And she's asking me all the time: 'What's happened, what should I do? I'm scared about heading back to Nauru. If I go back to Nauru they'll kill me.'

"I don't want to lose my mum in detention centre, I don't want my mum to die in detention centre."

The family, which also includes the man's sister, has been held at Wickham Point since February last year, when they were brought to Darwin for the mother's medical treatment.

Doctor Peter Young, a former director of the International Health and Medical Services, who specialises in mental health, has been looking over the family's medical records, which the ABC also has access to.

"They [the records] show people who have been subjected to the detention environment, and the negative effect it has on their mental health," Dr Young said.

"It signifies this person has been placed in a highly distressing situation for a prolonged period of time, which is what that system is designed to do. It's causing her to feel distressed and upset.

"From the records it's clear … that there have been serious concerns about her mental health."

Dr Young said the elderly were also a vulnerable group in detention.

"There's been a lot of attention to particular concerns about children as a vulnerable group in detention," he said.

"But what is also important to understand that detention harms everybody over time, whether children or other groups.

"A person who is as elderly person as she is, then that would be another type of vulnerability."

Dr Young said it showed the Australian Government was ignoring its own policies around the health of vulnerable people in detention.

"There are policies the Department [of Immigration and Border Protection] implemented some time ago in relation to the other cases where it was recognised there were problems in detention and a detention in health framework was put in place," he said.

"There was another policy about people who were seen to be vulnerable because of torture and trauma histories and those people should be treated in an expeditious manner and be put through the system as quickly as possible and they shouldn't be kept in detention for long periods.

"Those policies are still on the department's books and that's simply not being followed."

The Immigration Department would not comment on the family but said it was reviewing each case on an individual basis.

'She just wants to find community'

Daniel Webb, from the Human Rights Law Centre, represented the family and also led Wednesday's High Court case.

He said the woman should be released into community detention and that he had appealed to both Immigration Minister Peter Dutton and Prime Minister Malcolm Turnbull to authorise the move.

"This is a 70 year-old woman, she's endured a pretty tough life. She's spent the last two-and-a-half years in detention. She told me she just wants to find a community," Mr Webb said.

"She shouldn't be locked up, she particularly shouldn't be warehoused on the tiny island of Nauru.

"The stroke of a pen is all it would take our Prime Minister to do the decent thing, not return these vulnerable people to harm."

Sister 'ate washing powder to kill herself'

The man in detention said his sister was also dealing with trauma from her time on Nauru.

"Some security guards — one of the Nauru officers — he wants to abuse my sister. So she didn't say anything, she was embarrassed and ashamed," he said.

"After a few days, she tried to commit suicide and she ate washing powder."

Mr Webb said the younger woman was terrified of returning to Nauru because she "could come face-to-face with the guards who threatened her".

"It's simply inexcusable to send this woman back to a place where she has already suffered such serious harm in our care," he said.

Family separated by Rudd government policies

The family arrived on Christmas Island in mid July 2013, which coincided with the date the previous Rudd government tightened up policies on boat arrivals and offshore detention.

The son agreed to go to Manus Island, leaving his sister and mother at Christmas Island, because he said he was promised they would join him after two weeks.

"That was an outright lie," he said.

He said he was not allowed contact with his family for several months and negotiated to go to Nauru as a family.

Dr Young said he was not surprised by this description.

"The government was very keen to get people offshore to demonstrate that they'd put this new type of detention in place as quickly as possible … they needed a group of people to go and they chose at random the group of people," he said.

"That was something which was very difficult for people to understand, 'Why send me when the guy next to me you don't send?'

"They were told things that weren't true about how they'd be processed. All to help them agree to go quietly. And then once they arrived, they found out things were different to what they were told."