I recently helped a friend move, and drove her car with the cat for about 7 hours. She tried to give him something to calm him down (ask your vet about it), but we hardly got him to take any before we left. We didn't want to frighten him any more, and agreed to just try and see how he does without it. He was meowing somewhat in the beginning, but actually calmed down quickly. I had him in his carrier on the passenger seat an talked to him a lot. We stopped twice and put him in his litter box (the one he was used to).
If you don't want to take that chance, maybe you could stop by your vet on the way and have them sedate your cat. That's what I did, when I had to take my two cats on a 17 h plane trip. I went there on the way to the airport and she gave them some tranquilizers. They slept almost all the way. If you do that, you have to make sure your kitty is safe in her carrier, because she will be sleeping and may not notice if stuff around her shifts or falls. You should also watch if she is doing o.k. from time to time.