It's not entirely required to know anything about programming to create 3d models for games. But I'd recommend for your wife to understand the basics of how your game will work (Mostly how it renders the models, etc).

There is a difference with creating game specific models, mostly from file format, polygon count, Triangles vs Quads, Textures, etc.

I'm an avid Lightwave user myself, and I highly recommend it, but the price can deter many people.

I have used Wings 3D and it's a nice package; a good tool when first starting out with 3d modeling. Blender is very powerfull but has a steep learning curve.

I'd recommend checking out MilkShape 3d, and Gmax. Both are designed specifically for game modeling, they are easy to use as well as powerfull, and are widely used in commercial games.

There are many more free 3d packages avaliable, and I'm sure you will find one that you like.