Give a treat before and after. Take your time and make sure she is relaxed before ending the session. Get your pet used to the motion of the moving car. Once she is used to the car running without any fearful reaction, back the car to the end of the driveway, then forward again to the garage. Give her a treat and praise her.
Repetition is the key.
The more you do this the more confident your pet becomes that cars are no problem. In fact, to her it becomes a great place for attention, praise and even treats. Now it's time to take a short trip around the block. Treats and praise before and after, and calm, reassuring talk throughout the ride are a pre-requisite. Gradually increase the distance traveled until your pet is calm no matter how long she's in the car.