Talk to your vet about getting some ace or maybe some chlorpromazine for your kitties. I don’t like to drug my girls, but given the choice between that and dealing with one screaming and the other puking for 10 hours, I’m going with the drugs. This might not be a viable option depending on the age and health of your cat, but it’s certainly worth checking into.
Keep her in her carrier if the car is in gear. It’s safer for everyone involved. You do not want to try to pry a cat ass out of your face doing 75 down the interstate with semis all around you, nor do you want her to decide to dig her claws into you under those circumstances. Nor do you want her to go flying through the cabin if you have to hit your brakes. It’s much better to fly five inches into the wall of the carrier than a few feet into the windshield.
How’s she going to react to being the carrier that long? Well, a lot depends on how she deals with the carrier on shorter trips. If she hates the carrier and shrieks inconsolably while pissing everywhere when you box her up for trips to the vet, you’re going to want her a little something. If she does pretty well with the carrier, things go should much more smoothly.
As for food and water, I wouldn’t give her any while you’re driving. I’d feed her the evening before you leave, then pull her food when you go to bed. Take her water away when you get up, then keep her NPO until you stop for the evening. Again, feed her, then take her food away at bedtime. Letting her digestive tract empty out before you get rolling will keep her from vomiting or shitting everywhere (trust me, you don’t want to try to clean cat puke or diarrhea off the cat and carrier at a rest stop, nor do you want smell said mess while looking for a place to stop) and greatly reduce her need for a litterbox during the drive. And don’t worry, a healthy cat isn’t going to become malnourished or dehydrated over the course of a day.