Harmony Bryant, 26, was found on the brink of death in bushland near Bonny Hills, about 25km south of Port Macquarie in NSW on August 16, 2003.
But her death was not treated as a homicide for four years.
Ms Bryant was killed when an unknown person set her car alight.
Sustaining a broken pelvis, a fractured wrist and left arm, and burns to 60 per cent of her body, she was quickly taken to hospital.
Her car, a Hyundai Excel, was found on fire about 200 metres from the road.
She spent a month in hospital before dying from her injuries on September 19, 2003.
Police believe she fell off a nearby cliff before being brought back to her car by an unknown person or group of people.
A 2011 inquest found she had died from burns caused by a person or persons unknown.
Ms Bryant's death has plagued detectives for years since, and one of the state's top cops admitted to reporters that early examinations of the incident were not up to scratch.
"The initial investigation was treated as a motor vehicle accident and a fire, and no suspicion was raised at that time," Homicide Squad Commander Joe Doueihi said.
"Things could have been done better."
Her death would have continued to be treated as non-suspicious if her family had not conducted their own investigation into the incident, according to the coroner's 2011 report.
The officer in charge made his incorrect assessment despite many unusual features, the coroner found, and did not change his report even after receiving information suggesting something was amiss.
As a result, opportunities available in the "vital" 48 hours after she was found had been missed.
Ms Bryant's mother is pleading with those who know more about what happened that night to come forward and provide information to claim the reward.
"Her father knew from the time he went to the site that this was no accident," Karen Bryant said on Thursday.
"Unfortunately, he passed away eight months (ago) and he didn't get to see his suspicions acknowledged."
"Today you have been offered one million reasons to come forward."
Police believe the young woman booked accommodation for two people at a nearby caravan park but the second person has never been identified.
No one has ever been charged and no new persons of interest have been identified in recent years, Det Supt Doueihi said.
The NSW government and police in 2011 offered $100,000 for information about Ms Bryant's murder.
But with the reward increased tenfold, Ms Bryant's family and police are hoping they will finally get some answers about what happened to her nearly 23 years ago.
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