I actually struggle with carpal tunnel problems on account of running impact guns and having hypothyroid problems, and with that said, a larger comped 9mm is a kitten in terms of recoil, in particular if you shoot only standard pressure ammo.
Another note on ATEi, in terms of carpal tunnel issues, is that I personally have bouts of my left hand not being able to cycle a slide when it gets cold at the range in the winter due to my screwed up wrist. The slide serrations for the purpose of cycling a gun one handed against your pants are really nice to have for this issue, as well as of course if your hand ever gets injured.
FreeinAZ, a cheaper budget option would be a 9mm Glock C model, which will work decently enough right out of the box. They just aren't as reliably good fitting as a M&P.
If she goes the mouse gun route, the critical thing is to have a good and long barrel, and the hottest ammo available. The 32 is a bit better, but the smaller 22 and 25 models are low enough in penetrating capability that they should be thought of as direct contact weapons best suited for soft tissue paths to the brain, such as through the eye sockets, nose, mouth, maybe below the chin. The neck would be a "good" option too. Shorter barreled 25 and 22 pistols have this nasty habit of causing the skin to break before bouncing off someones skull. Performance wise, if it comes to actually having to stop a bad guy, we're probably talking about an awful lot of hand to hand stuff before the bad guy actually gets stopped, because not a whole lot of bad guys are going to stand still while a defender puts a baby browning in their eye socket.
A 6" barreled 22 with the hottest and heaviest ball ammo, a 32 with Buffalo Bore ammo, these things will penetrate better, but will still sorely lack stopping power. And all that is why I would strongly suggest a nice and soft shooting 9mm.