So sorry...well, first of all, contact your doctor for sure.
If he/she thinks it's motion sickness, and is okay with the following, try them. I get horrible motion sickness and here's what helps me...
1. Don't give Emily books or toys in the car. If she gazes through the windshield, it might help. I know it seems impossible but just point out things that are in view of the windshield.
2. Keep snacks in the car (no sugar) like crackers or other crunchy/salty carbs. If you approve, a little gingerale can be helpful.
3. If your doctor thinks it's okay, try giving her a little candied ginger. If you're going on a trip longer than 20 minutes, just offer a little nibble periodically.
4. Try to travel during naptime. Put on her favorite bedtime cd to encourage a nap.
Good luck and congrats!