Joanne Marie Gill, of Alberbury, near Shrewsbury, died on May 21 this year when she was involved in the crash on the A458 at Churncote.
Mrs Gill, 50, was driving her Vauxhall towards the Shrewsbury by-pass when she entered the lane of oncoming traffic, her inquest at Shirehall heard.
Her car collided with the back of a Range Rover Evoque and rotated in the road, also hitting a Nissan Navara parked in a lay-by. A Land Rover Discovery was also involved in the crash.
Mrs Gill, who lived with her husband and two adult sons, was pronounced dead at the scene.
The hearing was told that road traffic collision investigators found no defects with the cars involved, or the road itself, and weather conditions were good.
Mrs Gill's husband said she had suffered a brain tumour, but had been given the go ahead to drive.
He did not understand why she would have lost control.
John Ellery, senior coroner for Shropshire, Telford and Wrekin, said there was no suggestion that she did it deliberately, and he discounted that as a theory as there was no evidence to support it.
He said: "She lost control for an unknown reason."
He concluded that her death was caused by a road traffic collision.
In the aftermath of the tragedy, Mrs Gill's son David paid tribute to his mother and thanked the passers-by and paramedics who tried to save her.
"It means a great deal to us that, although she could not be saved, she was not alone and that people were with her," he said.
Mrs Gill was married to husband Phillip and had two sons, David and Phillip junior, and a daughter, Jacky. She was also a grandma to Bethany.