Iram Shahzad, 32, admitted two charges at St Albans Crown Court after Spencer Bell was killed as he tried to help a man who had fallen from a bridge.
Mr Bell, 71, died instantly when he was struck by Shahzad's car, in January last year.
Shahzad was sentenced to 14 months imprisonment, suspended for two years.
The court heard the mother of three had sped up to the scene of the tragedy and then tried to get round the slowing cars.
Travelling at speeds of between 82 and 88mph with two of her young children in the back of the car, she realised at the last moment the way ahead was blocked by two stationary vehicles.
But instead of stopping like the other drivers, Shahzad thought she could beat the hold up by swerving back into lane two.
Her car then hit Mr Bell, an ex-policeman and charity worker, who had gone to the aid of Alan Trethewey, 67.
Mr Bell died instantly, the court heard.
On Friday, judge Martin Griffith told her: "This case is a tragic case for the family and friends of Spencer Bell."
He said the term Good Samaritan was frequently over-used but in Mr Bell's case it was a fitting description.
"Nothing I can say or do can fill the void left by this splendid man's untimely death," he told her.
He disqualified her from driving for 18 months.
Mr Bell's wife Wendy told the court: "My life has ended. Once it was full of laughter and giggles, chatting all day long and happiness. Now it is misery, sadness and tears."
Sebastian Gardiner, defending, said his client was truly remorseful and her driving that morning had been out of character.
A woman who killed a Good Samaritan when she struck him in her car on the M1 motorway has admitted causing death by careless driving.