I've got the same issue with my spouse...it crushed me when I finally realized that flying wasn't going to be a family event for me, especially up here in AK, where getting away from the road system is what it's all about...
In addition to the stuff above, there are a couple physical/mental training programs that you can try to use...both on the idea that you get motion sick up to the point of puking, stop and recover, and then do it again. Eventually, the time it takes to get sick exceeds a normal flight duration, and then you just get more and more used to the motion, and less prone to sickness.
One program is called "P.U.M.A", it's a commercial thing that involves DVDs and the above technique. (link:
http://www.aircraftspruce.com/catalog/p ... umadvd.php). It didn't work for us.
The other is something the military uses, called a Barany chair (google it...). It's a chair that is mounted on a hard base and swivels. You sit on it, the "doc" spins the chair around while you close your eyes and tilt you head around...basically get the fluid in your ears moving in different directions than what the nerve endings in your ass are telling you. The doc can alter the speed of the spin and really get you out of wack. Anyway, when you can't take it anymore, you stop the spinning, and try to relax your body back to not-sick status, then repeat the process for about an hour total. Do this a couple times a day I think, and eventually, your body gets used to the otolith organs disagreeing with your seat-of-the-pants and eyesight/horizon senses, and all is well. My wife threatened me with a bat when I tried to get her to do this...it also didn't work.
Good luck with the search, hope it turns out better than mine...just be prepared to embrace ground based family adventures.
Karl