I'm reminded of a saying of one of the saints, (and I'm paraphrasing): "Preach the Gospel always and, when necessary, use words".

My wife and I are both attorneys. I started experimenting with the GTD methodology thanks to serendipitous product placement at my local Barnes & Noble. (Prior to that I know nothing of it). As my wife saw me getting more and more efficient, effective and relaxed, she started asking what I was doing to get there. I just sensed that the idea of a "clean sweep and dump" (getting everything into "in" with the permission to not have to complete it all right then and there) would resonate with her. And it did. From there she's gotten into the next action context-based lists, project lists, etc.

My advice would be to simply model the system, and try to get a sense of which phase will hit home for her, and start there.

Good luck.
(And don't forget, "encourage spouse to GTD" should now be on your Project list!