I just wanted to say that the fact that you felt a strong urge to write the song shows that you empathise with this woman. It seems to me that if you empathise so strongly with her then you're not exploiting her, particularly when you continue to question your moral responsibilities to her. You said - "The letter from our mutual friend asked for my prayers, but my immediate response was not to pray but rather to think, "Hey, I should write a song about it". This seems to me to be your way of thinking about her - isn't that pretty much what prayer is? I don't think you're exploiting her, but I do agree with KB saying that you must be aware that when singing the song there may be people that it's particularly painful for.