Police are still trying to determine how and why Aashima Goyal, 19, exited a fast-moving car on the M1 at Dapto, about 15 kilometres south of Wollongong, seconds before she was struck by a truck and killed on September 25.

The University of Wollongong commerce student, who lived in the Campbelltown area in south-west Sydney, was a passenger in a car being driven by a 20-year-old man from Barrack Heights, south of Wollongong.

Police said their vehicle had swerved on the motorway immediately before Ms Goyal, a former East Hills Girls Technology High School student, tumbled out of the vehicle during peak hour.

A number of vehicles swerved around her, but police said a tipper truck was simply unable to avoid hitting her. She died at the scene of the crash.

Ms Goyal's father, Praveen Goyal, who runs a migration and education business in Sydney, said he had taken his daughter's remains back to India, where her extended family had performed prayer rituals to celebrate her memory.

Her family had held a ceremony at the ancient city of Haridwar​, on the banks of the Ganges River.

"You are my angel," Mr Goyal wrote on a website set up in memory of his daughter.

"I know you are at peace with God and I am missing you. But don't worry as your memories are keeping me busy and every single moment I am spending with you feels meaningful.

"I thank God for blessing me with a child like you Aashi. And, I thank you even more for giving us 20 years of happiness. You have not gone anywhere. You are in our thoughts – you are with us as always. You live in our hearts in a sanctuary and no one can take you away from there."

Mr Goyal said he was telling devastated family and friends to "remember your good company, your caring nature and your beautiful smiling face".

Ms Goyal's mother, Neel, wrote: "Lots of love and hugs to my lovely, bubbly and caring daughter. May God give you peace and you stay in His vision to remain always protected. But we'll miss you a lot. Love you."

A university friend, Heidi, wrote that she would miss seeing Ms Goyal, a "beautiful, friendly girl", around campus, while another friend, Brie, said it was difficult to "say goodbye to someone who thought you still had many hellos".

"Words don't describe the pain that is felt now that such a sweet person is gone from this earth," Brie said.

"I will always remember your loving nature and beautiful sense of humour. You may not be here physically, but in spirit you live in our hearts forever. I send my love and thoughts to your family. Rest easy beautiful girl."

Last week, Acting Inspector Kylie Macfarlane, from the Lake Illawarra Local Area Command, said the circumstances of how and why the woman left the vehicle at high speed still had not yet been determined.

Investigators would examine the days and moments leading up to the crash, which occurred at 7.45am on a Friday.

Acting Inspector Macfarlane said the investigation, carried out by detectives from the Lake Illawarra Local Area Command with involvement from the Crash Investigation Unit, was expected to take a considerable amount of time.

At the time of the crash, Inspector Wayne Starling said the truck driver had tried to avoid hitting the woman but simply couldn't.

The crash occurred on a section of the motorway with a speed limit of 100km/h.

"Several vehicles took evasive action to try to avoid hitting the female. Unfortunately one couldn't - just didn't have sufficient time," he said.

"It's horrific for police, but even more so for the family and friends; it's just horrific for them."