Jeeze. That's a tough set of circumstances.
I've got arthritis really bad myself and a lot of hand and wrist problems, but at least my hands are full size for a man. Also, I've got prior handgun experience.
I can't say for sure what would be best for her, but I can tell you my best guesses based on my experiences. Then have her try them at a rent a gun range if possible.
First the don'ts, then the maybes, then the likely candidates:
Do NOTs
.357 Mag revolvers shooting .38s have low enough recoil for me, but those guns are way to big and heavy for a little lady with small hands. There's no way she's going to like those.
I've found the .38 Spl small frames are murder on my hands. Those are out. Even in stainless steel or steel at a weight of 23 oz they are out. I really like the Taurus 3" barrel small frame .38 Spl, but my hands cannot take it even with standard pressure ammo. So I can confidently recommend that you forget about small frame .38s. Sorry.
The Beretta Bobcat .32 is miserable for me. This is mainly due to the difficult trigger pull. Remember that she has probably a weak finger. The recoil really hurt my hand. I can't recommend the Bobcat.
The Walther PPK/S I tried had a horribly difficult 17 pound trigger pull and a very difficult to pull slide. Additionally Walther is known for jamming with hollow points. I can't recommend Walther.
I do not recommend any .22 LR handguns because the stopping potential is pitiful. I think this would be worse than no gun.
I do not recommend a .22 Mag auto because I feel that the rim fire makes misfires a possiblity and that is a problem with an auto. Also, the rim itself may make failure to feeds more likely.
Maybes
I'm quite fond off .22 Mag 4" barrel revolvers because they offer good penetration and some expansion. I think some decent 3 round stopping potential is offered from a 4" barrel revolver. The 2" barrel versions
don't have the velocity to be good for SD. I like 4" for SD, but not 2".
.22 Mag revolver trigger pulls are at the top end of my tolerance. I recommend she test some of these out. Taurus makes some really nice 2" and the best 4" with 8 rounds. I'm wearing the Taurus 4" right now. The 2" barrel .22 mags are all small frame and would fit a small hand perfectly (but little stopping potential from a 2" barrel). Unfortuneatly, the trigger pull is stiff on all rimfire revolvers, which may be the deal killer here.
Ruger SP101 .32 Mag with 3" barrel is an excellent gun for recoil senstive people. It has the best and lightest DA trigger pull out of the box of any revolver I've ever tried. It's a dandy gun, but the grip is a bit small for my hand. That might mean it'd fit the lady's hand perfect. The only problem is that the recoil is right at the top of my tolerance on my good days. On my bad days the recoil is too much for me. Therefore, I don't know if the lady could handle the recoil or not. It's borderline on recoil. It's also a bit heavy to conceal and carry.
Likely Candidates
I really like my Firestorm .32 ACP. I suggest she try a Firestorm .32 (made by Bersa, but imported and assembled in USA by Firestorm). It's a dandy and much better than a Bersa because the Firestorm's have rubber grips and are available in .32 ACP (as well as .380).
This small, thin, single stack gun is just about ideal for a person with arthritis and small hands. The slide and trigger are very easy. Safety is not easy, but can be carried with safety off.
I just ordered a Bersa high cap .380 that is a steel frame weighing 30 oz empty. It has a 15+1 capacity. This should have very little recoil, fair stopping potential, and lots of ammo. However, I'll put Firestorm type rubber grips on it. I ordered this from
http://www.impactguns.com/store
This gun sounds ideal for a person with arthritis, but I haven't shot it yet. The double stack grip will be wider. So that might not be good for small hands. The slide and trigger are very easy. Safety is not easy, but can be carried with safety off. (I handled one of these guns in my local gun store)
I just learned of the FN 5.7 pistol. I want to learn more about this gun. It sounds ideal for a person with arthrits and I think its stopping potential should be around a .380, but with less recoil and more ammo. However, I'm no expert on this gun. I'm still learning about it myself. It should be an ideal gun for me since it should also fit my hands.
I think the FN 5.7 pistol would also be ideal for this lady, if it's not to large for her hands. If it is to large, then I recommend the Firestorm .32 ACP.
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Money
The above were recommended without regard to price. The FN 5.7 is expensive at $850. The other best choice is the Firestorm .32, which costs $250. The Ruger SP101 .32 Mag cost me $400 at my local gun store. I don't think the SP101 is quite as good for her as the FN 5.7 or the Firestorm .32, but maybe she'd like the SP101. Those are local gun store prices. They would each be about $50 less money if bought online.
If money is an issue, then the Firestorm .32 is the only option. It's a darn good gun. I like my first Firestorm .32 matte black so much that I bought a second one in nickel.
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Bottom line
For shooting the FN 5.7 would be best if it fits her small hands, but it might be too big. The Firestorm .32 would likely be very good for her and is easily affordable, small and easy to carry. For a house gun the FN 5.7 has great potential for this lady. For a carry gun the Firestorm .32 is best.
At least those are my opinions. As a handicapped shooter with arthritis, I think I can understand the lady's problems pretty well.