That's a toughie. Usually the first .22 is an "understudy" for the "main" gun -- a 22/45 or conversion slide for a 1911, for example. I don't know of a .22 that replicates the handling and manual of arms of the XD.
Single actions like the Ruger 22/45 and Buckmark duplicate the grip angle of the 1911, and so don't have that Luger look, but with their light single action triggers, they invite AD's by people just starting to learn, like your wife.
A Smith & Wesson kit gun (they make several variations on the J-frame .22) is a good beginner's gun, because of the double action trigger. The titanium frame weighs nothing, but costs a lot. The stainless steel version is dandy, too. Neither, though, replicates the feel of the XD.
You might want to look at the Walther P22. It's as close as I can think of to the look and feel of the XD.