It sounds like she may be getting motion sickness and the motion sickness is causing the behavior issue. It may not be causing her to vomit, but is making her uncomfortable. Motion sickness is worse if you can't see out a window. Some people use Benadryl to calm their dog before car travel and Dramamine is also used for motion sickness, but your Vet should be consulted before using Dramamine.
Benadryl can be given to your dog, the dose is up to 2mg per pound every 8 hours. The dosage for Dramamine (Dimenhydrinate) for motion sickness is 2-4 mg/pound by mouth every 8 hours.
Any medication should be given an hour in advance to car trip.I have a dog that used to constantly pace and jump around the car as well and no training would help, but Dramamine helped even though he wasn't actually vomiting.
For anxiety, herbal rescue remedy is often used, but another option is a DAP collar that uses pheromones to calm a dog. It emits pheromones similar to those produced by a mother when nursing pups. You might try giving the medication, waiting an hour and then put her in the car and just move up the driveway slowly so she sees that it isn't the same as it is normally. She may still be anxious since she is used to it making her uncomfortable, so I would still use a DAP collar so she is calmer as well.
If these were not the medications you were thinking about, please respond.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time.