Good suggestions all around, really, but here's my two cents: My wife was at best cool to guns when we started dating, but I took her to the range, taught her the basics, and then turned her loose with Ruger MkII Target and she had a great time. She's now an awfully good shot, has four pistols of her own, and is showing an interest in rifles.
That said, she has a soft spot for the MkII/MkIIIs. Also, she dearly loves her Walther P22. So, I'd say you can't go wrong with those.
In addition, I'd have to throw in another vote for the M&P22 because, while the wife hasn't fired mine yet, she is really pleased with her fullsize M&P (the ergos on these things are great; I *love* mine), and the 22 is literally the spitting image of the fullsize. I've held both pistols side-by-side, and there is no discernible difference in weight or size and the controls are all the same; you'd be hard pressed to tell them apart just by feel or from a distance. So, it could be a great stepping off point for moving up to something larger later; it would make for a near seamless transition to any of the M&Ps or the Shields. Plus, it's actually made for S&W by Walther and when you strip it down, it is essentially a modified P22 wrapped in an M&P's clothing.