Such judgement is premature. There are numerous potential aggravating circumstances that can be remedied.
ETC(SS) raises some good points... Perhaps you could put the car in ready mode and have her sit in the car in the driveway in front of her laptop, or with a book for an hour or two to make sure it's not something other than motion sickness? Oh... and what's the condition of your suspension?
I found that I got motion sickness while driving my Prius early on, however I don't have any problems now. I think a big part of the problem for me, was that I wasn't used to driving a car with huge A-pillars, like the ones all newer cars have. I found myself sorely missing the thin, crumple-like-foil-in-a-wreck pillars of my colt vista. It's like part of your peripherial vision is cut off. I would suggest your fiancee try to adjust to it first, give it at least a month or two, before taking a big $$ hit on the car.