Welcome.
Let me begin by letting you know that you can do a search on this subject (lots of threads on women's carry), which should be good research material.
Just from your description, it sounds like she likes the handling/recoil characteristics of a bigger gun (i.e., Glock 17) but needs/wants a smaller gun to tote in her purse (like a snubbie revolver).
Smaller guns are going to produce more felt recoil, which she probably won't like, but bigger guns are going to be heavier and harder to conceal.
My best suggestion is to have your GF try as many different guns as possible to find one that fits her hands, has the least unpleasant recoil characteristics for her, and fits her/your budget.
My second-best suggestion is to convince her to work on her upper-body and her grip strength, as that will allow her to comfortably manipulate/shoot a wider range of guns.
As for the Shield in 9mm, I have carried one for about two years now, and like it a lot. It's small and slim, extremely reliable, yet has enough weight to mitigate a lot of the recoil, and it's more than accurate enough for defensive purposes.
All of the women that have shot my Shield like how it fits their hand and its small size. Most don't mind its recoil, and only one has had any 'limp wristing' issues with it so far. That one is 4' 10" and 96 lbs. soaking wet. She has virtually no grip strength and had chronic issues with her Bersa (stovepipe/FTF/FTE at least twice per mag). The problem isn't nearly as bad with my Shield, but she managed to jam it up twice in a 50 rd. box.
Possible issues w/ Shield: trigger pull weight is on the heavy side, making quick follow up shots a matter of some extra practice, if she doesn't have much grip strength. Though not anywhere near as heavy as a brand-new j-frame revolver trigger. Also the double captured recoil spring makes racking it a bit tougher for people with less grip strength. Loading the magazines also is not easy until the mag springs break in a little. I recommend the Uplula magazine loader, though they are more expensive than most competitors (retail approx.: $30). Other mag loaders will do the job for less, if not as comfortably.
Other suggestions to rent/borrow:
Ruger LCR in .357 mag. I believe the .357 mag version is heavier than the .38 spl version, which should help some with felt recoil, plus the trigger pull weight is about half what most j-frame snubbies offer (talking about brand-new examples; used ones may have lighter pulls through 'experience'). Should be able to find a used one for $350-$450, I think.
Ruger LC9S: this is a striker-fire model, so lighter pull weight, smaller than the Shield, same capacity, I believe.
If she likes something like a Glock 43, then maybe something from the Springfield XD line. Out-of-the-box XDs typically have lighter trigger pulls than comparable S&W M&Ps/Shields. Probably can find a used one at or under $400. I think (I'[m not as familiar with XDs, sorry) she would want to look at the XD-S line.
Fortunately for you/her there are currently dozens of guns that'll probably fit her needs, so it's just a question of getting her to pull some triggers and decide what she wants.
And don't worry you'll get lots more responses soon enough.
Good luck and good hunting.
Bingo! DaleA remembered it for me; that corneredcat site should be a big help to your GF.