I'm gonna break ranks and say that you are thinking correctly for the answer for your wife. I went through this very thing with my wife and I also tried to steer her toward a semi-auto. We tried the Shield, the XDs and the Ruger LCP. She is not a "gun person" but did take some lessons with all of these. The problem is that while we enjoy handling semi's and dropping mags and clearing jams, etc. some do not and factually, most women are in that group. Even the basic "racking of the slide" does not come natural and easy for most women. I am not saying all but most. So, in a moment of fear or excitement it is not a good time to experiment with this question when her life hangs in the balance.
So, we tried several revolvers and she ended up with, and still carries, the Ruger SP101. This revolver is a bit heavy, but it's mass is a friend when firing and shooting .38 caliber rounds with a very mild recoil. It is crazy reliable and has a buttery smooth trigger.
Semi's do give more rounds but while stylish, must be handled with frequency to be comfortable and reliable.
As Clint Eastwood said as "Dirty Harry"...."That's a helluva price to pay for being stylish."