As Georgit79 says, it helps to keep looking at something in the distance, preferably ahead.
This allows your body to understand the joggling better, and is why few people get sick when driving themselves. Let her drive more...?
Motion sickness happens when the signal from your inner ear doesn't match what you see. Looking steadily at something inside (like a book or map) is always worse, as your vision is too steady for the movement.
I find any more than quite a small amount of alcohol makes motion sickness worse -- unless I've had so much that everything is moving anyway, when I'd feel sick regardless.
Motion-sickness tablets can be good, though I think they can stop you driving safely.
Some people are just lucky about this. I'm not too bad myself (except when at sea in a small boat, below decks). One of my daughters seems bombproof -- she'll happily read for hours in that same boat, in a chop. She was never sick as a baby, either.