Moff - cats are so funny. If they have been badly frightened, they can stay in one place for a long time. My first cat had crawled into my old stereo cabinet when I first moved into a new apartment. I thought he had escaped the apartment. Turns out he was in there for over two weeks. I about died one morning when out he came - brazenly asking to be fed.

Is it possible Winnie is up inside the underpart of your car - and the dogs have frightened her? Maybe put some food under the car and see what happens. (far enough so that a dog couldn't reach it.)

Just grasping for straws here.