Out of curiosity,
mosue52, how old is your wife's M&P 9?
For a while, they had mechanical accuracy issues, which was eventually traced to the barrel, IIRC.
As for the Gen. 4 Glocks, as many have noted above, their initial troubles are now just part of the gun-world lore. Yes, they had teething issues when they first came online, and yes, those issues were very real, but of my training-heavy friends who have purchased and seriously run their Gen. 4 Glocks over the course of the last two years, none have reported any problems that would be considered outside the norms for any other quality defensive handgun.
And overall, if your wife does get the shopping bug again, I strongly second
haertig's advice above:
And to go one further, even: to not just handle them at a gun-show or at a store, but to actually rent the guns at a range or beg/borrow/steal

friends'/family's so that she can actually try them out, live-fire, at the range.
Why the latter?
Because putting your hands on a gun is just like sitting in a car at the dealership showroom or on a car-show floor. Until you take that test-drive, there's traits of the vehicle that just won't manifest themselves as the car sits there, inanimate.
It takes a very, very, very experienced shooter to just be able to pick up a gun to say whether he/she will more than likely "like" to shoot it, or not.