Marion, you have received excellent advice here. But I guess I would ask a few questions of you. First, you obviously have some level of uncertainty and/or discomfort about publicly performing/recording this song. What/why exactly is that? Are you afraid of doing harm to the person the song is about? Are you afraid to ask permission to use the song, for fear they may say no? Are you afraid of appearing to others as if you have exploited this person just for the sake of a song?

Now, by asking those questions, I am not trying to suggest that any of the above possibilities are the reason for you asking this question, because I don't know you. But in order to put yourself at ease about it, I think some honest self-examination is in order, so you are clear about what is making you feel uncertain or uncomfortable about all this. Once you know and have admitted that to yourself, it will be much easier for you to make a good, confident decision about performing/recording the song.

You have to satisfy yourself first, as a writer. Writers SHOULD feel uncomfortable when righting about living people whom they make characters in their work. It is that feeling of discomfort and unease that acts as a check and balance against being exploitative, manipulative, libelous, etc. It is that place of unease from which springs the integrity of the artist.

Good luck with it. Thanks for starting such an interesting thread.