I absolutely agree with the KISS principle. It appears to me you have it covered pretty well. Have you tried to get her to exercise the hands a bit to increase strength? Anyway, my wife has the same problem (she’s 71), and may have to switch to a difference firearm. We tried out the S&W M&P Shield, and it seem to be accurate, reliable, and the slide was easy to retract. If you don’t mind them, Cheaper Than Dirt has them for less than $400.
We also are “shooting” for commonality of calibers. Primary for us at this time is 9mm in Glock 17 (may change for the wife) and AK’s firing 7.62×39. We do have other calibers of rifles and handguns, but those are the primaries. Of course, she also has a 20ga and I have a 12 ga shotgun. And we each have a .22 rifle, her’s is a Ruger 10-22 Take down, and mine is a Ruger 10/77 bolt action.