creative way to raise passenger seat

First off all, how far does it have to be raised? Is it that she's short enough that she can't see out of the windows? The only thing that I can think of that would still be considered somewhat safe would be to fabricate/weld, out of steel, a frame that duplicates the seat frame and raises it to the desired height. This new piece could be bolted to the car where the seat was, then the seat could be bolted to this frame.

Cheapie fix, use oversized bolts as washers/spacers. Too cool fix get the mechanics from another drivers seat (ride height is adjustable)

This actually has me wondering and thinking about seeing how hard it would be to fabricate one up. I just built my own hanging Tire Rack for about $40 (it hasn't fallen off of the wall yet, loaded up with 4-17" tires) and I don't think this would be much worse, maybe a few more angles. I'm with you though on the Safety aspect. I think spacers could shear off in an accident if the proper torque and clamping forces weren't applied. A welded structure though would almost act like part of the car. Another thing to consider is going to the junkyard and see if you could find the brackets/rails from another seat. Modify these brackets with some cross supports, bolt the brackets to the floor, then bolt the seat to these brackets. The only problem with this is the height may be too high. Another safety consideration, raising the seat height, you are changing the center of gravity for the seat/occupant. I don't know what that would do in a crash, but I'm sure it changes. To be the safest, I would think you would be able to raise the seat to the same height as what the drivers seat goes. Hopefully you figure something out, because there's nothing worse than your wife being jealous over another woman (oopps I mean car)!

Good luck!

Just buy longer bolts (grade 8) and install some spacers under the seat frame mounts.

Have you seen what the seats are bolted to? Unless, it has changed, THIN sheet metal that will give way before any spacers or bolts.