There's a sticky at http://forums.buckeyefirearms.org/viewtopic.php?f=6&t=10097
that you should have a look at, but it's not mandatory. It's also somewhat sleep-inducing. Don't go past about the third page unless you're into agony. I should have cut that thing off, but we were having fun
About your question: I don't believe in Glocks (
), but if you must, it's a good choice. The S&W Shield (9mm) may be a good choice, too. Avoid the .40 Shield - nothing at all wrong with the gun (I'm wearing one right now.) But the various "full power" .40's may be a bit too much for your mom. IMHO, the 9mm would be more comfortable. Same, I think, goes for Glock.
The S&W "M&P" series guns - the M&P9 and 9C - are fine choices, too, IMHO, but carrying the full size versions is a little iffy for smaller people. 'Bout the only difference is that the .40's are a lot easier to shoot than the .40 Shield.
Stay away from the Kel-Tec's.... I have a P3-AT, which is a very tiny .380. For a good couple of years, I was never able to get a full magazine through it. Something would break, or I'd just give up due to the pain. OTOH, my daughter's buddy has a 9mm Kel-Tec that's been 100% for him, and is fairly comfortable to shoot.
Gun stores like to sell super-lightweight .38's or .357's. They carry fairly well, and are very small. But DO NOT try to use them in .357 Magnum, or +P loads. You only have to try that once.... For Self Defense, an ordinary .38Spl round is quite sufficient, IMHO.
If you can find a .44Spl wheelgun (don't even think about .44Magnum for her!), they're as good as a .38Spl, and only slightly tougher to shoot.