Waders, I applaud your sensible approach to your mom's request. Good for you.
As usual, we have a bunch of folks on here recommending one handgun type over another based on their own biases. Most of this advice is next to useless.
Any certified handgun instructor who has significant experience with women as neophyte handgunners knows that the approach to each one of them has to be highly individualized. Women don't approach these questions with the same kind of logic men do. This doesn't mean they're illogical, they just have a different kind of logic based on different primary assumptions and different values. Don't try to steer a woman toward one type of gun or caliber. Just let her shoot several types, let her decide which type she likes best, and answer any questions she asks with as little bias as possible.
The way I approach this question for ANY woman is to let her try a few guns to get started, then based on how she likes those, narrow the search down some. You can go to a gunshop with an attached range that rents guns, or you can gather up some of your own guns and some of your friends' guns, whichever works better.
The first set of guns to try should all be smallish in grip frame and size, and loaded with light-recoling ammunition. I usually start with a K-frame 38 Special revolver (M65 or M66 or equivalent with 3-4" barrel), a Glock 19, and a single-action 9mm of some type, typically a 1911 clone. Ammo should be 38 Spl wadcutter loads for the revolver, and WW USA 115 gr standard pressure for the 9mm's. Let her shoot 6-20 rounds with each of them at a silhouette target at 2-3 yards distance. With the revolver, have her try both single action and double action firing. With all of them, have her load them and cock the action, put on the safety if applicable. Let her work with the manual of arms, not just the firing aspect of operating the gun.
After you've fired the 3 test guns, see which she prefers. If she likes the S&W revolver, the search is over. Get her a stainless K-frame and some GDHP loads and she's good to go. If she prefers the Glock or the 1911, you could either just buy her a Glock, or let her try a few other autos such as the S&W 6900 series (which A LOT of women LOVE due to the small gripframe and short trigger reach, very light recoil, etc), a Kahr 9mm, a Beretta M9, a Browning HP, etc. Give her some frame/grip choices to work with (eg, G19 vs G26). If she's got her heart set on a 45, then by God let her try her chosen frame/action type in a 45. Let HER make the choice as to what's suitable for her. If you do your job right, she'll make an appropriate choice.
If she doesn't like any of the above, I'd go along with jwp's recommendation and let her fire the little Beretta Tomcat. It's a helluva little pistol, very easy to operate and fire, and surprisingly accurate. Friends don't let their friends carry mouseguns, but in the case of your mom it's probably okay.
I almost guarantee you'll be surprised at what gun she'll pick. Just let it go. Make sure she shoots it enough to get happy with it.
