Yeah, it's gonna be up to what she can comfortably hold, shoot, and conceal. Does no good if she can't carry it easily and ends up leaving it at home.
Have her shoot some "standard" weight .38 snub revolvers; Taurus/Rossi models should come in at or under that price range, as do used S&Ws and Charter Arms pieces. Many say that the "lightweight" versions may be a little too snappy for some people. Ditto for the pocket .380 pieces, like the Kel-Tec P3AT. Again, if possible, she shoot get some shoot time with whatever she's considering.
My wife cannot effectively hold and cycle the trigger on my Bersa Thunder. On the P-3AT, she can, but her wrists, barely bigger than a garden hose, likely would not provide the resistance needed to keep the slide functioning normally. She's truly one of the few ladies who is not easily suited by a handgun much bigger in caliber than, say a .32 auto, or bigger in size than a P-AT (or P-32.)
I don't know how petite your mom is, so, as the say, your results may vary.