She spotted the robber, dressed in black with a black hat on or hood up, in Friars Court around 5am on Sunday.
The woman told a community Facebook page she screamed at him and he fled in a silver car parked further up the street.
She wants to warn other people in the area to be on their guard and posted: “Make sure your cars are locked, people.”
Others on the Facebook page said their vehicles had been targeted nearby, in the vicinity of Hillhead Community Centre.