I think Walther PPK is an excellent gun, I have an Interarms and a S&W, nice size gun, though not a pocket gun. They both shoot very well, but that first shot in double action can be difficult, it is a very heavy trigger on the first shot. I'm sure with some effort it could have a little lighter trigger pull, and for a steel gun, it's a great choice. Other .380's to consider are the NAA Guardians, very simple design and a good choice for a steel DAO gun. Polymer guns, my first choice would be Ruger LCP, very lightweight, very compact, great pocket gun.
The rule of thumb when buying for your wife is to buy something 1/6th of the cost of your carry firearm like a high point or a derringer...ok jk ...you should take her to ITP or a friend with a variety of handguns and let her try about 10-15 handguns to see what she likes....my wife prefers a glock 19 and hates revolvers and berettas but your mileage may vary
S&W 38 special revolver - Airweight or bodyguard. If she is going to let it slip around in her purse loose, she will not be able to find it quickly if she needs it. Anything without a double action like striker fired pistols just might go off when her many items eventually slip inside the trigger gaurd. You would hate to have her digging for her wallet and have a lipstick punch a round off inside the store, or anywhere for that matter. Many of these guns are built to be ready to fire, and the holster is considered the primary safety when it is not in your hands. I like the one with either the barbed hammer or concealed hammer so there is nothing to snag on her purse as she is trying to get it out. If it happens to not fire, she simply pulls the trigger again and it rotates another loaded round in place and fires. No worrying about recycling a slide, no worries about a stove piped piece of brass needing cleared from a jam. Revolvers are very simple, and very reliable. Should she have an injured wrist in the future you can perform all operations with one hand unless you need to reload, and even then an injured wrist might not be able to pull a slide back on an auto.
I guess my first question would be what kind of other handguns do you have at present so I know the overall types of ammo you stock. I have taught several women how to shoot at this point, and always start them off with a .22 and work up from there.
If your Mrs didnt care for the sub compact, what about just a decent compact 9mm? Ive fired the Ruger LC9 compact and found it to be a great hangun!