Why not get someone to do that for the old woman? Isn't she living with someone who can operate the tablet? If she is then let the person play her the audio books whenever she needs to listen to them.
Or you could just remote control it, probably via the internet... or set it up to play automatically at a particular time daily.
I would have recommended some old people-friendly devices for playing digital files but I'm not sure you can find them in your country.
Perhaps an MP3 player? But which one?