Phil,
Again I find myself agreeing with your sentiments,and I assume that Leo has checked that the fan belt is neither snapped or lose.
I have reread the original post and can find no indication of the distance of the car to home journey she has to make.
My understanding of a car alternator is that its function is to replace the initial drain on the battery that the starter takes out and then retain the charge which ,as you point out will be less if you do not use radio, air con etc.
My intial suggestion of using a fully charged battery to jump start the car still stands, I was not suggesting that it be connected in permanently and could be used to jump start the engine again should the existing battery fail en route.
HTH
John