The temperature had dipped to 10C by 8am, contributing to the woman's serious condition - but incredibly she was in "good spirits" when St John Ambulance arrived about 8.45am.
"She had lots of cuts, a hip injury and a chest injury, she was obviously very cold but quite conscious and in good spirits," St John Hawke's Bay district operations manager Stephen Smith said.
The car was balanced against a tree on its side until morning when family members discovered it some time after 8am.
The Napier Fire Service also attended and first had to secure the car, before freeing the elderly woman from her 15-hour ordeal.
"She wasn't physically trapped but it's encased her and she couldn't get out," Mr Smith said.
"We had to be very careful about the way we extracted her, we had to secure the vehicle before we could do anything."
He said while they weren't overly common, there were other accidents in which people were trapped for long periods, adding that in this case the woman had been fortunate to make it through the night.
"I think she's very lucky to have survived - it was very cold," Mr Smith said.
Napier Fire Senior Station officer Bryan Dunphy said it was a "technically difficult" rescue because they had to work around the tree and unusual angle of the car.
"We removed the roof and managed to get the woman out ... the car was probably about 15m down, it was quite a big drop - I can't imagine it would have been obvious [from the house above]."
Relatives gathered at the Puketapu Rd home yesterday and were being assisted by victim support.
"They are all supporting each other," Mr Ormerod said.
Senior Sergeant Greg Brown said the name of the woman's deceased husband would be released at lunchtime today.