It's been a while since I have shot a M&P 22, but I would take that one if the gun fits your wife's hand. The Ruger is more likely to work with people who have smaller hands, because it generally is has a smaller grip and also comes with two grip adapters.
The Ruger has a weird manual of arms with the DA/SA, and a frame mounted safety that you have to push up to disengage. The latter feature can be confusing to someone used to pushing frame mounted safeties down and slide mounted DA/SA safeties up. Then there is the DA/SA transition. The top 5 or so rounds stagger funny in the magazine and some care has to be taken when loading magazines. Also, the Ruger I have shot seems to prefer full power "box of 50" ammo to bulk pack, which could be problematic from a supply standpoint at least in the short run. The M&P ran fine with bulk pack.
One downside to the M&P is that the sights are more of a combat style, with a wide gap in the rear sight that leaves a lot of light when the front sight is centered. That should be ok for a plinker, though.