You can give the dremamine (spelled right?) motion sickness pills, just check w/ your vet for proper dosage.
Also you can get her used to the car slowly. Take each step slow & very often preferably a few times a day. First start off by just sitting in the car w/ her, then just start the car, then just back up to the end of your driveway, then to the end of your street then around the block. Ignore the nervousness & wild behaviors & PRAISE all calmness!
Also try to bring her to fun spots, like the pet store, the park etc...
Good luck