Good question & the choices are almost overwhelming without more info, so the following is a list for new handguns by top tier manufacturers that should be good to go out of the box, although not all these are hammer fired. If your wife's hand size allows her to comfortably handle & shoot a full sized gun:
S&W SD9VE, Walther PPX, Ruger 9E, maybe SIG 250 if you like the trigger
If she has smaller hands, maybe these single stack guns (slightly thinner grips) will work better, but remember that the smaller & lighter the gun, the more recoil will be felt:
S&W Shield, Ruger LC9, Beretta Nano, Walther PPS, & maybe Taurus 709 Slim (it has very good recent reviews).
The Nano can have the mag release switched to the left, but - sorry - I dont know about the others.
All these are current production, modern guns that will need less care & maintenance than some of the other, older used choices (I'm a gun guy, so I prefer those older designs myself). And I didn't mention several manufactures that make fine guns at lower price points - they generally need more break in, maintenance, etc. Again I have several of those guns, but they might not be the best choice for those who don't like tinkering on guns.
Finally, even though you mentioned 9mm, would you consider a revolver? A used S&W Model 10 (.38 special) is absolutely dependable, simple to operate & shoot. There were about 6 million made, so you can find them in good shape within your budget.