The retired teacher is a Villawood Detention Centre volunteer visitor who has spent more than a decade supporting vulnerable young men seeking political asylum.

In that time the silver-bobbed grandmotherly figure, now in her 70s, has earned a reputation as a feisty guardian angel when it comes to springing detainees who have reached breaking point.

Petersen says she had no idea what to expect on her first visit and nobody could have prepared her for it.

"To this day my heart still sinks when I walk through those three locked doors ... I get the same feeling just thinking about it," she says with a shudder.

At the initial check-in there is little familiarity, even after 12 years. Visitors are prohibited from carrying a driver's licence, camera, phones, documents and uncooked food. It is a 220 km fortnightly round trip from Petersen's home and she has never taken a sick day.

"If you tell them you are visiting, you never let them down because they get dressed for the occasion and count the seconds until you arrive - some come running towards you and then cling to you when it's time to go," she says.

While Petersen is happy to provide detainees with moral support, she has gone light years beyond that.

"They all have their own story but I suppose the most fragile of all was a young man named Sumon," recalls Petersen referring to an Indian student who over-stayed his visa when he got word his parents and sister had been killed in violent riots at home.

"I visited him one day and couldn't find him anywhere so I entered the living quarters where you are not supposed to go and found him cowering under his bed consumed by anxiety."

Months later, after Sumon closed himself in a cupboard for four days, he was sent to a psychiatric hospital in Queensland for severe depression. Petersen continued to visit.

"I couldn't believe it when I heard they were going to send him back to detention ... I knew if that happened he would kill himself," she says.

Petersen strenuously argued his case with immigration officials and eventually had him released into her care in her own home.

He was one of four men for whom she did the same thing and eventually helped to dramatically turn their lives around.

Petersen, born in the Macleay Valley in northern NSW, grew up with an innate sense of social justice going back to the day she got her first pay as a student teacher at Kellyville Public School.

"There was a group of us including one male, a lovely guy but he probably did the least work in our group. When we compared our first cheques, as we were paid in those days, we discovered he got more money than us women because he was male," says Petersen.

"I thought it was a mistake at first but when I found out it wasn't I got myself along to the Teachers Federation meetings and joined the campaign for equal pay."

Petersen gravitated towards people who shared her enthusiasm for causes.

Her first husband, the late Bob Gould, earned recognition in the 60s in Sydney for his anti-conscription stance over the Vietnam War.

The last of his 11 left-wing bookshops in Sydney is now run by Petersen's daughter, Natalie, who also visits detainees with her mother.

Petersen's second marriage was to NSW politician, the late George Petersen, who in 1981 created huge controversy by initiating gay reforms in the NSW Parliament.

He called for the decriminalisation of sex between two consenting adults three years before it succeeded under the Wran government.

"We both copped it," recalls Petersen. "George was publicly vilified and I was subjected to countless vicious phone calls about the so-called monster I married."

Petersen says conditions have improved slightly since she began visiting at Villawood.

"If released they used to be shown the door with nothing but a blue plastic bag holding their belongings," she says.

That is how she got started. A neighbour came across a lonely figure on the side of the road outside Villawood in 2003 and when she discovered he had no money or home to go to she arranged for him to stay with Petersen's daughter - he remained there for a year.

"Some are now given Centrelink money to live on, which attracts a lot of criticism in the community but if they are not allowed to work they need something to live on ... they would far prefer the dignity of work," says Petersen.

Petersen, who has never sought the limelight for the work she does with detainees, is proud of the achievements of the four men she took into her home and now counts as part of her family.

Two, Sumon, and Bangladeshi-born Ali are now married and are highly respected registered nurses at separate Sydney hospitals. Fiezel, the youngest of the four, is a bright, chirpy salesman for Telstra who rings "Mum" Mairi every few months. The fourth man, Zahid, from Bangladesh, returned home after six months when Petersen helped locate what was left of his family. They regularly talk on the phone.

Petersen says her work with detainees has in many ways enriched her life. She has attended two of their weddings as an honorary family member - one in Bangladesh - and become grandmother to Ali's two children.

But she often despairs about the public discussion on asylum seekers in Australia and what she perceives as a reflection of a society whose members don't fully appreciate how lucky they are.

"I think everybody should be able to visit centres like Villawood at least once so they can understand a little better before they make judgments."