I'd suggest you take her to as many gun shops or gun shows as you two can find, and have her "try on" as many guns as she can get her hands on. It's just like buying shoes..... you may not like what I wear, and they might not fit you "just right". When she finds some that feel right to her, then check and see if she can cycle the action.
If it doesn't "feel right" to her, she'll never shoot it enough to become proficient with it.
i would suggest the xd9 in the 3 inch, it is small and compact and if necessary comes with the added mag extension in case you decide you want to carry it or shoot it or if she has a really big pinky finger or something. i would also suggest modifying the weapon, replace the guide rod with a canyon creek or even a don's and change the 16 lb spring to a tactical load of 20 at least even 22 if she can rack with slide with that weight, it reduces the kickback on the recoil and the weapon cycles slower, less felt recoil. if you change out the trigger for a trigger kit it reduces the pull about 50% and gives you a better pull. magloc also makes a recoil rest so that your thumb rides high on the weapon so that the recoil isnt as bad because the weight on the back of the weight keeps the barrel down
I just completed this little dilemmna with my wife. Although she can shoot any of my handguns from .40 - 44 cal, rifles form 22 to 30-06 and 12 G shotguns she in the end had to select the handgun of her choice. My wife is 5'2" tall and has small hands. In the end she opted for the PF-9 Kel Tec. It is light and small enough to go in her purse and the feel of the gun fit her well. Recoil was manageable, and above all the pistol is small and light enough for her to carry regardless of weather/season. Hope this helps.
I love my XD9 SubCompact! It's a perfect fit for my hand and is small enough for me to carry on my slim body. I have a service model before and the grip stuck out too far and I printed more than a newspaper factory.
As said above though... Take her to a gun store and let her handle as many as possible. Let her work the slides to make sure she'll be able to do it. If you're lucky, maybe you can hit a store that will allow you to rent them so you can shoot some rounds through the ones she likes (some ranges might offer this)... My GF hates the recoil on my SC vs. the Service she shot before. She also thinks the slide is 10x worse than it was on the service.