I'm sure that someone more knowledgeable will help out. But - I think you should let her in the car give her a treat and let her out. Don't even shut the door. Do that for a week and then shut the door and stay there with her for 5 minutes. Then stay for 5 minutes with the car running but don't go anywhere. Then go in and out the driveway. Then maybe a mile. If she is really afraid you might have to go even slower. Or she might decide after a week that cars are really fun and you'll be all set.
Effie (GSD) 7-20-11