, Welcome to JustAnswer. I'm a licensed veterinarian and I'll be happy to help. This is actually a pretty common problem.
Medically you can give Dramamine. The dose is 4-8mg per kilogram of body weight. Dramamine is good trips because it does cause some sedation. The dose then should be repeated every 8 hours.
Desensitization often works also. This means that you start with very short times in the car and then gradually increase the time. At first just put her in the car minute or two, but don't go anywhere. I'd try this 3 times daily couple of days or until getting into the car is not upsetting.
The next step is to turn the car on while she is in the car, but still don't move.
Then, you drive a very sort distance like down the driveway and back. Repeating each step often until she is less anxious, and then gradually increasing the length of her trip should be effective.
Desensitization does take time, but is usually successful!