NSW mother refuses to leave husband's bedside after crash that killed their teenage daughter.

The mother of a young learner driver who was killed in a crash in Sydney’s northwest has spent the night at the bedside of her critically-injured husband.

The two were involved in a collision between a Suzuki Swift and Falcon sedan at Glenorie around 4.50pm Friday, which killed 19-year-old Jodie Gillet at the scene.

The girl’s father, Gary, aged 58, was supervising her at the time and was taken to Royal North Shore Hospital in a critical condition with multiple injuries.

Preparing to sit her driving test, witnesses said Jodie Gillet performed a U-turn when the collision occurred.

Ms Gillett’s grandmother Heather has since told The Daily Telegraph that the family is still trying to process what has happened.

“She would never go over the speed limit,” she said.

“She was just so conscientious. We don’t want to lay any blame. Jodie was kind, caring and a beautiful girl in every sense. This shouldn’t have happened.”

Seven ambulances and a medical helicopter were sent to the scene at the time, but could not save the 19-year-old.

Chief Inspector Frank Gilroy said the incident was a reminder for all drivers to take care on the road.

“(It’s) absolutely tragic when these things occur,” he told reporters on Saturday.

“Naturally mum and wife was absolutely devastated. She’s been at her husband’s bedside since last night.”

“It’s absolutely tragic when these things occur — all drivers should be aware to take care,” Mr Gilroy said.

Several witnesses attempted to help the victims and have since spoken with police.

One of them, David King, said he tried to talk to the pair to keep them conscious through the car door.

“You couldn’t open the door, you couldn’t do anything,” he told the Channel 7.

"She died right in front of me."

Mr King said he rushed down to help as soon as he heard the crash.

"She's about the same age as my daughter, so that hit hard. Too young."

The driver of the other car, who was not believed to be seriously injured, has undergone mandatory testing, including drug and alcohol testing.

Police are urging anyone with information on the accident to come forward and call Crime Stoppers on 1800 333 000.