Willow's 6th Sense: "Arf! I see a live person"

This really happened yesterday:  We decided to take a ride to the mountains after we dropped off our car at the Tidwell Ford for some work.

Anna left the house in the Ford.  She had to go by Krogers  so I gave her some time before Willow and I left.  I did not know how much time to allow .  We just went after I gave up looking for my map.

On Chastain Road we stopped at a red-light.  From Old Canton Road, which goes by Krogers Anna  entered Blackwell Road and we fell in behind her.

Willow saw her car and started crying for her.  We could not see Anna in the car but I knew it was her by the license plate number and a magnate sticker about dog rescue.

I don't know how she knew it was Anna but she did.   Sound of the engine?  License plate number?