Well, first of all, as others have said... you need to discuss with her exactly what she wants or doesn't want. If she doesn't want to be babied, then that's that. If she doesn't like diapers -- and many women don't -- then again, that's that.
Secondly, there are many in-between levels. I first explored diapers with my then-girlfriend in college, but I wasn't her "baby." It was more like a BDSM arrangement, and of course I was the submissive partner, but we talked EVERYTHING out in advance and kept up the communication throughout. I think that's really the critical thing. We never did anything that I or she would be uncomfortable with. (Actually, we still talk, more than a decade after we broke up.) So the point here is... what does your wife actually want? And also, do NOT try to "ease her into" anything that she doesn't express a want for. Fair warning, that will backfire.