The woman, who asked to be referred to as Bev, had been leaving a Slimming World Session at St Bartholomew's Church, Penn, on Monday when she saw the attempted theft taking place.
She told the BBC she saw her car being loaded onto the back of a transporter truck and jumped onto the back to reverse her vehicle down the ramp by releasing the hand brake.
The driver fled the scene after a brief tussle with Bev, in which he tried to take her keys.
Passersby stopped and took the number plate of the truck, with Bev saying the incident came a few months after a catalytic converter was taken from her husband's car.
A spokesman for West Midlands Police said: "We’re investigating this attempted theft.
"We’ve spoken to the owner and contacted a local church who may have the incident on CCTV.
"Anyone who saw what happened but hasn’t yet contacted us should get in touch.
"If you’re worried about your car being stolen, visit our website west-midlands.police.uk for security advice from the experts."
Contact police on 101 or via Live Chat at west-midlands.police.uk
Alternatively, contact Crimestoppers anonymously on 0800 555111 or at crimestoppers-uk.org