Since your mother is not recording music, just spoken voice, go for a dedicated voice recorder rather than a music player with a voice recorder fitted as an afterthought. They are more likely to feature hig/low sensitivity switches, recording activation based on sound level (VCVA) and so on.
The Olympus WS series is very compact, can hold several hours of recording even at the highest quality setting, and lasts seemingly forever on a single AAA battery (or rechargeable). You just unhook the battery module to expose a USB plug that goes straight into the PC. I have the mono WS-110, but I recommend spending a little more for one with stereo capability (you don't have to use it if you'd rather save disk space) and microphone level meters on the screen.
The Olympus WS series is very compact, can hold several hours of recording even at the highest quality setting, and lasts seemingly forever on a single AAA battery (or rechargeable). You just unhook the battery module to expose a USB plug that goes straight into the PC. I have the mono WS-110, but I recommend spending a little more for one with stereo capability (you don't have to use it if you'd rather save disk space) and microphone level meters on the screen.