He said the boyfriend had rushed to a nearby home to raise the alarm about his injured girlfriend.
"He was very upset. I would say she died instantly,'' Mr Millard said.
The car had spun as it veered off the narrow road and the driver's door crashed into the stump of a branch that had been left when the rest was cut off several years ago, Mr Millard said.
"It was terrible,'' he said.
"Had she been a metre either side, that branch ... would have either gone into the back seat or over the bonnet.''
Mr Millard said the boyfriend had a large close family that lived in the district and his grandmother was at the scene shortly after the crash.
Police said their investigation was ongoing to "establish the cause of the crash''.
Courtney's death has been referred to the coroner.