I'd have your wife shoot one of the smaller 9mm's prior to purchasing one. A while back, I took mine and her friend shooting. They tried a number of pistols and it gave me some insight. I had them try a Bersa 380, Sig 232, S&W Model 638, S&W Model 27, M&P Compact 9mm, CZ-75B.
Contrary to what the internet says, recoil on all of those .380s was pretty light and the grips and trigger reach were proportional. The Bersa was a borrowed pistol and I was very surprised at how well the ladies shot it, they didn't have much trouble racking the slide, either.
Long story short, they thought the steel 9mm was too heavy, the revolvers trigger pulls were too heavy to control and thought the M&P compact in 9mm had too much recoil. (We were using 115 grain target loads.) Going into it, I was confident the 9mm's would win out, but both preferred the Bersa and Sig 232 by a wide margin.
Also consider mode of carry. These two ladies did not have a wardrobe that would accommodate anything other than purse carry. For purses, they didn't like any of the conceal carry models...less than ideal to have a 5 lbs striker fired auto with no safety carried in the same compartments as anything that could snag the trigger, keys, etc. For off body carry, a pistol with a safety might make some sense, in the case of a purse snatch it might take someone a second or two to figure out how your pistol works.