Anne Jones, 44, told the trial of two men at the High Court in Glasgow how she and her son, Connor, 20, pursued three masked men after they got into a blue car after the raid on Eric N Smith Jewellery in Newton Mearns, East Renfrewshire.
Mrs Jones said she followed them for a brief time before losing them.
Mrs Jones told the trial: "I waited till they passed my car and then I followed them. I didn't know what the road was so I put my sat-nav on and discovered it was Eaglesham Road.
"After the first bend in the road I could still see them, after the second bend I couldn't see them at all … I lost them."
Alan Mitchell, 34, and Gary Mitchell, 20, deny robbing the jewellery shop of a quantity of watches in April this year. They have lodged special defences of alibi.
Earlier Mrs Jones told the jury she was sitting at traffic lights and pointed out the jewellers' shop as being a nice building.
She added: "I saw three men coming round the corner with their faces masked and one was carrying an object that looked like a concrete lintel on his shoulder. I knew something wrong was happening."
Mrs Jones said her son phoned the police, and when the lights turned green she turned into Eaglesham Road. When she saw the robbers driving off she followed them.
Her son told the court he noted down the registration number of the getaway car and gave it to police. He added: "My mother followed the car while we were on the phone to the police, but we lost the car after the second bend in the road. It was travelling at speed."
Mrs Jones was not able to identify any of the men.
The trial before judge Lord Jones continues.