The colleague was concussed and stuck in the passenger seat so her daughter, who is 18 weeks' pregnant, climbed the hill to flag down cars for help.
She managed to find her phone and call another workmate who was also heading home to help as well as the police.
Police, fire and ambulance attended the scene and both occupants were taken to Hawke's Bay Hospital to be checked over but had no serious injuries, she said.
"She's all right, the baby's all right.
"They are lucky they are all right, no major injuries. They came off quite lightly."
If the car had been any smaller, if it had landed in a nearby pond or if anyone had been in the back it would have been a different outcome because the boot had been crushed into the back seat, the mother said.
"It's a very dangerous stretch of road.
"The farmer is used to cars ending up there."
Her daughter's workmate, who had been driving ahead, had noticed the road was a bit slippery because of recent rain.
People needed to be careful, especially heading into winter, on that stretch of road because there had been a number of crashes, she said.
A police spokesperson said they were called to the incident at 1.20am and it was dealt with within an hour.