S.W.
Some people use a DVD player to distract their child, but sometimes that has an opposite effect (it has something to do with the motion outside the car through the peripheral vision while watching a movie). If you use a DVD player already, try not using it next time and see if she gets sick. If you don't use a DVD player, give it a try and see if it helps. Also, where is her carseat located? If it's in the middle, try moving it to one side of the car so she can see out the window better. If it's on a side, try moving it to the middle and see if that helps. (sometimes just being able to watch the road or passing objects can help).