They believe she may have been the first victim of notorious serial killer Ivan Milat and say had police made the connection, he could have been stopped much earlier in his lethal campaign.
Ms Rowland's younger brother, Steve Rowland, will be among those appearing at a NSW parliamentary inquiry into unsolved murders and missing persons between 1965 and 2010, beginning on Thursday.
Milat died in 2019 while serving seven consecutive life sentences for murdering seven backpackers whose bodies were found in NSW's Belanglo State Forest in the 1990s.
His possible connection to Ms Rowland's death as well as the deaths and disappearances of scores of other young women will be examined by the inquiry.
Chair and instigator of the inquiry, NSW Legalise Cannabis MP Jeremy Buckingham said he believed Milat's murders date back to the early seventies and potentially Ms Rowland's death.
"I think that there's a building body of evidence that Ivan Milat was responsible for many more murders than he was convicted of," he told AAP.
In a submission to the inquiry, Ms Rowland's family said they hypothesised her abduction and murder was sexually motivated and may have been the start of Milat learning his predatory behaviours.
Ms Rowland disappeared on February 26, 1971 after spending the evening at the Canberra Show. She was aged 20 and was five months pregnant.
She had arranged to travel with her sister, sister's fiancee and another friend to continue the night at a venue in Canberra's north, with the trio travelling in one car and Ms Rowland alone in another.
At some point during the journey the vehicles became separated and the group lost sight of Ms Rowland, assuming she must have changed her mind and gone home.
Ms Rowland's car was found abandoned later that evening and three months later a dog walker discovered her body in a pine plantation outside Canberra.
The family claim at numerous junctures police could have connected Ms Rowland's death with Milat, including in the weeks after her disappearance when he was arrested for the alleged abduction of two women near Goulburn, north of Canberra, one of whom he allegedly raped.Â
Mr Buckingham said policing had come a long way, but in the past involved a bias against some victims including Aboriginal people and people from alternative backgrounds.
"Policing has clearly improved over the decades, so this isn't about any criticism of policing now," he said.
"What we want to do is understand why these crimes weren't solved and how serious they were."
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