My better half came to the range for the first time in 8 years, and fired my teenage son's Mod 17 Glock 9 for the first time. She has very little handgun experience. Even with a proper two handed stance, she felt like the the Glock (with the smallest backstrap) was about to slip out of her hands under recoil with factory ammo.
Any ideas as to a 9 for someone with small hands?
Thanks in advance.
Way I see it you have two problems, which may or may not be actual problems.
First, is your wife FEELING like the gun will slip out of her hands. Is this because the gun ACTUALLY was at risk of slipping out of her hands? Maybe, but probably not. My 12 year old niece can fire my double stacked .45 unsupported no problems. At the time she was probably 4'6", 75 lbs (not sure), with the hands of a little girl. At no point in time did she look, or say that she felt, like she was about to lose control of the firearm. Here's the ru

I have oversized grips on the 45. Her hands had less than 50% coverage on the available surface area of the grips. Holding it one handed is like holding the family bible. I did not have her shoot THAT one handed.
I take you on your word that she had a proper two handed stance, so I would want to explore why a proper stance did not make her FEEL like she had a good grip. (Maybe modifying the grip slightly could allow for better feel and recoil management) Many female police officers with your wife's stature can shoot the Glock without issue, one handed, on both strong and weak side. I am not convinced that your wife NEEDS smaller grips in order to ACTUALLY control the firearm. As a confidence booster you can try having her shoot it one handed. I have often coached new/young/small shooters who share this fear of the gun flying out of their hand, and those fears typically go away once they shoot one handed weak side and don't have the gun come flying out of their hand. Firm grip, lock the wrist, no bend in the elbow, she will be fine. I wouldn't start off that way, but it shouldn't take very long to work up to it.
The second problem, is enjoying a comfortable grip, which we all know plays a huge role in performance. Assuming she did have a proper grip, and still didn't feel comfortable, then grip geometry more so than size may be a factor. Only suggestion there is to get out there and shake hands with as many different guns as possible and see what feels right. She is the only one who can say for sure what feels right, and its why there are hundreds of different models out there.
Personally I hate Glocks because the grip feels like I am holding a square 2x2 piece of lumber, and being balanced towards the top side due to the light weight polymer frame, feels a lot snappier in my hand than the 1911 or a full framed 226.