My recommendation would be 9mm given both it's wide range of power choices, depending on loading, as well as manageable platforms from which to launch it. 380 isn't bad by my standards but it can be a bit snappy given the blow back design most 380 pistols are build on and the typical light weight and small size of those weapons. That smaller size may also make manipulating controls and slide racking more difficult for someone with hand strength and flexibility issues. A good example of a manageable 380 would be the Beretta Cheetah given it has a little more weight and heft to it.
The 9mm offers a lot of flexibility in countless platforms and I would think a decent none +p hollow point out of a handgun size and type she can hold comfortably would be about ideal. If still too much then powder puff 115 gr FMJ's could be used. Not ideal but in bunches placed in the right spot on the target will still get the job done. As a second choice out of a wheel gun a none +p 38 special in a large to medium frame gun could work as well. Again staying away from the ultra light weight and smaller examples would be best. Good luck and hope this helps.