The ute skidded 30m down a hill, across a lane of traffic and into a ditch, crashed over a concrete post and rolled, coming to rest with her body suspended by her seatbelt, with the driver's door facing up.
Ms Griffiths said she unbuckled her seatbelt and managed to stand up in the cab of her boyfriend's Nissan Navara as it lay on its side.
She turned on the light and could not find her phone.
When she tried unsuccessfully to open the driver's door overhead - and the handle came off - she panicked, she said.
She realised she was trapped. ''I could see lights going past and I wondered why no-one was stopping,'' Ms Griffiths said.
Michael Williams was travelling back from Dunedin to Balclutha with his wife and teenage daughter on the damp night.
If he had not been stuck behind a tanker travelling 70kmh-80kmh on the winding, hilly section halfway between Milton and Balclutha, he, like other drivers, might have missed her, he said.
He thought he saw a light, but when his daughter said she thought she saw a number plate, he did a U-turn and went back.
Mr Williams said he was just ''in the right place at the right time''.
''When I went up there she was screaming to get out,'' he said.
''The windscreen was all broken ... I just kicked it out of its rubbers and pulled it apart and she slipped out of there pretty quickly.''
Mr Williams was on the phone with emergency services when the car caught fire.
Nothing inside was recovered.
Ms Griffiths had been on her way to Balclutha to pick up her boyfriend before heading to a 21st birthday party.
Instead, she was rescued by a man who turned out to be the father of one of her good friends. She was lucky, she said, to have only hit her head and suffered some whiplash.
Ms Griffiths said she first heard Mr Williams asking her if she was all right and if she was the only one in the vehicle.
While she was trapped inside, she did not know smoke was coming from the ute. She did not realise the extent of the damage until after she got out of the vehicle, she said.
''It was all smashed. It was pretty scary once I was out of it.''