Jane Marion Lord, 76, had tried to stop her red Vauxhall Corsa from rolling down the driveway at her home near Newcastle Emlyn, Ceredigion.
Miss Lord is believed to have died on 21 December 2016 but remained under her car until a friend, alerted by her dogs, found her after Christmas.
A coroner at the Aberystwyth inquest concluded her death was accidental.
The inquest heard how Miss Lord, who lived in the village of Cwmcou, was last seen alive at around 19:00 GMT on 21 December at a party at the house of her friend Francesca Lis Ross.
Miss Ross said she first became worried about Miss Lord when she went over to her house on 23 December, to give her a Christmas card and found the house locked but the car still on the drive.
"I assumed she must have gone away with a friend with a vehicle, so I left a present down at the house and left," Miss Ross told the inquest.
Miss Ross returned with her husband and two dogs on 30 December after trying to call Miss Lord the day before.
They broke through the door of the house to check inside and searched the garden, but only found Miss Lord's body when the dogs took an interest in the underside of the car.
PC Matthew Fraser, of Dyfed-Powys Police's forensic division, described how Miss Lord had suffered crushing injuries to her shoulder and hip.
He added that hand marks on the car suggested she had tried to stop the car rolling down the drive before falling over and being pinned under it.
PC Fraser said the car's handbrake was in full working order, but that the "three clicks" the lever had been set at were only just enough to stop it from rolling down the driveway on most occasions.
He said five clicks of the handbrake would have engaged it fully, but that Miss Lord would have found it difficult to pull the lever this high.
Ceredigion coroner Peter Brunton said Miss Lord would not have survived the night of 21 December.
He added: "This is one of the those dreadful cases where if circumstances had turned out slightly differently we wouldn't be here today."
A pensioner was crushed to death under her car and lay undiscovered for nine days, an inquest has heard.