Hi Seasons,
I forgot to respond to your question. When/if she calls, let the machine pick it up. Do not sit there and listen like a little deer in the headlights. Turn down the volume so you cannot hear what she says, then delete it without listening.
If she calls again, do the same thing. Again and again. If she ever gets to speak with you or some member of your family, say that your machine has been acting up. Act cheerful and vaguely apologetic but do not accept any abuse about it! Well, try.
Your approach ought to be that you changed your schedule around and waited for her and then she did not show so you figured she was with one of the many other people who have offered to help her. Tell her you are not upset that she did not show, you forgive her, no problem.
If she blasts you, allow a little pause, then say, "you sound so angry. is everything alright with you?" If she lists all the terrible things you have done, say, "is that what is making you so upset? That I didn't wait for 2 hours for you to show up or phone?" Then just leave it there. DO NOT APOLOGISE. If you like, you can quietly disconnect the line while she is ranting. It is your phone, your life, your time....get it?
When she talks, you do not have to listen. She is not saying anything you need to hear, ever. In fact, quite the opposite. Ignore her raving, ranting, abusing voice. Let her be the voiceless one for a change.
Good luck
Plucky