you don't want a .40 in an apartment environment
walls are too thin
yes to all the readers - all the guns are powerful but let's minimize the probabilbity of hitting someone in the other room
is your wife strong?
can she rack the slide on a semiauto?
if so then get a 9mm either glock or XD
there are several manufacturers of bullets that are frangible or "safety" to stop quickly
if she cannot...
then get a revolver: either a S&W .357/38special or a 44mag/44special
HAVE HER USE the 38specials OR THE 44specials. they are mild and a lot of fun to shoot.
The 357 and 44mag is for your own personnal fun ourside of the apartment- hehe
these two have a lot of versatility in terms of energy - they cover all the bases