I have a few kiddos who are very prone to car sickness. We normally drive overnight to relieve them of some of the awake time. I can not ride in the back of a car myself. completely miserable is an understatement so I know first hand what the kids feel like.
Having said that, we just tried Bonine (commonly given for peole who get motion sickness, car or plane or cruises) and my kids were estatic! Neither of them were sick at all the entire 16 hour trip up to Maine in 12 passenger vans and then a week later, back again after some fevers/flu stuff while they were there.
Bonine is actrually a brand name. It is meclezine25 miligrams. It comes in adult and childrens versions (chewable cherry tablets.).
The kids had absolutely no side effects at all using this. The problem we have had with dramamine is they get headache, dry mouth, super sleepy and a few other symptoms from time to time.
So yeah, as a large family of 6, we often have to drive if we want to go. And we have to have kids "in the way back" as they say as we drive a van.
Give her a trial run before you take your trip and see how she does with it.
Oh and the two kids who are the worst sufferers, they even feel bad just riding to church on Sunday mornings for 1/2 hour- 45 minutes so pretty same scenario. We know all about the wipes and plastic grocery bags and such.
I second the no milk but do keep hydrated with sips of water, seems to help.