It seems that we cannot drive in our car for more than 15 minutes before Sonia throws up. (Car sickness runs in Aarti’s side of the family.) I’ve looked for solutions to ease the nausea online, but so far, I haven’t found much help.
I’m now planning to keep a bucket and clean-up items in the car for future incidents. There has to be a better way…
-Krishna
(On the plus side, Sonia’s been toilet trained for the past several months.) 
My mother’s cat has the same problem…if you find a solution, hopefully it will work as well for felines as it does for humans. She hasn’t found anything that works yet. (Thankfully, there’s less cause for the cat to take a trip in the car.)
try dramamine. Its for air/motion sickness, and is commonly available at any walgreens/cvs/pharmacy around. I dont know the child dosage, but the pharmacist should be able to assist.
My sister uses Dramamine and it seems to be effective. I used to have the problem but I find watching the world outside the car helps. Try playing “I Spy” with her to get her to look at things outside the car.
Have you checked babycenter? Here’s a page with some tips: http://www.babycenter.com/0_motion-sickness_1189999.bc
A gentle flow of air can help. I’m assuming Sonia is seated in the back, so, if possible, direct cool air back to her through the car vents. Or, rig up a small, battery or cigarette-lighter-socket powered fan to seat back in front of where she sits. Good luck.
I’m told that ginger pills work very well. Some of my friends swear by them for sea-sickness, which is another form of motion sickness. The suggestions of cool air & “I Spy” are also excellent ideas. If you do try Dramamine, make sure to give it to her 30 – 60 minutes before departing, otherwise, she will sick up the pill before the medication gets into her system. I’m not a huge fan of dramamine, personally, due to some of the potential side-affects. Including nausea, the very condition it is supposed to prevent.