The more I think about this, the more I think you should stop taking her calls. There is nothing of benefit to you or your parents in this situation, and who knows- maybe she thinks he owes her money or is the father of an out of wedlock child many years ago or something and wants to get his DNA from a hairbrush. Sounds like a great tv plot.
I fall in the “do what’s kind for everyone” category. You have no idea what she would say face-to-face and it would be inappropriate to allow her to see him now. So I agree, listening to her story would be reasonable and if she wants to write a letter to him you can offer to take it and possibly read it to him with the understanding that he will not comprehend it. And then let her politely know that this is closure on