Twiglet, our 3 year old Jack Russell, has car/travel sickness too. We tend to make sure the car or van doesn't get too hot and she has a towel etc to make a bed (more like a nest) in her crate. Dogs like crates because it is like a den.

We also like to do small trips in the car for a few days before a long one, she tends to cope better.

Make sure to keep her hydrated and don't make to much fuss over her if she is feeling down.