How does she act on your shorter car trips?  If she enjoys them or just lays down and goes to sleep, I don't think you have anything to worry about.  I would feed her normally too.  Nutrical is oily and is only a supplement or used to perk up a dog with low blood sugar in order to be able to eat.     
My dog loves to go for car trips and after a while just lays down and falls asleep.  I would just stop every few hours just as often as if you were at home or if you have to stop.  She should be just fine.     |