Kahr PM9 is as small as 9mm's come... 16oz... 6+1. Kinda snappy recoil-wise though, but, of course that's the trade-off concerning small size gun in a bigger caliber. It'd be good to get her to a range that rents guns to try out... 'cause it's a very personal, subjective thing. If she prefers the autos, gotta' make sure she can rack the slide OK on whatever one she likes... women often have a problem with it due to lack of hand strength. Best to get her to a range/gun store with a big selection and let her handle a bunch. (I'm sure you already know this, I'm just sayin'...) It often happens these days that husbands/boyfriends try to be practical and suggest .38 revolvers, but after shooting them awhile MANY women tend to want, and indeed get, autos.
Genitron.com: Details for Kahr Arms PM9 9mm Luger Pistol
BTW (for new shooters/owners)... ANY new autos, especially the small ones, REALLY need a good break-in... lots of slide-racking and at least 200 rds. to begin getting smooth and reliable.