If a German-made Walther is out of the question (because the German-made guns are the best of the lot), for one reason or another, then ...
The S&W model is a good choice (the added tang does make for a more comfortable shooter); so is the Interarms model.
But ... you can pick up the Manuhrin versions of these guns for under $450 these days, and they were wonderfully machined and perform to the same tolerances as the German-made guns. I'd start looking there, but only if she already has tried a PPK and is convinced that it's the right gun for her.