Tell her that it would be "terrible if something happen to your car while you were shopping." If someone did that to me, I'd probably move it as there is no way I would go inside and trust some lunatic not to follow up on doing something to my car. Nor am I going to stay outside for an hour and "out wait" someone.
PlateWire is a public repository and electronic forum of drivers by drivers. Using a drivers license plate, commuters can communicate their thoughts and feelings in regards to driving on today's roadways.