I will have to second the Benchmade Mini-Griptilian suggestion. It has a slightly under 3 inch blade, and it opens very smoothly and easily. The handle can be had in a wide variety of colors - green, purple, yellow, orange, blue - whatever your wife prefers. It looks small and innocent, (especially in bright colors) and will likely be "acceptable" to sheeple. It has a great grip for small hands, and a reasonable price.
The only other thing to consider is that you might want to get her something even smaller that she can put on her keychain, if she is the type that will otherwise never have the knife with her when she needs it (like my wife

). For recommendations on a keychain knife I will have to defer to others. Spyderco makes several. The mini-Superknife (made by Superknife) is even smaller, with replacable utility blades, although I have never owned one.
One more possibility - since this knife is a gift for a woman, and women like things that are pretty, you might want to consider the 3" Spyderco Persian (not the 3.5" Ed Schempp version, because of knife laws in your area, but the 3" version). It is a beautiful knife. I don't own one, but since it is a lockback I would imagine that it would probably not open as easily as the Griptilian. It also might not be as sheeple - friendly. But then again, some women appreciate something beautiful more than something practical. Depends on her personality.
Good luck and regards,
cds1