I knew the answer to the question’s of the song’s inspiration once, but my memory is rusty and my search skills don’t seem to be very good today. For now though, here’s what Wikipedia’s entry on “Taxi” has to say:
Also, the woman in the song “was gonna be an actress.” At the time he sees her, “she’s acting happy” in a nice suburban home, or something like that. In the same way, the narrator hasn’t learned to fly, except in his cab, when he’s stoned.
Okay, I may have dug up a lead on who the character “Sue” was based on. She may have been Clare MacIntyre, according to a paper by Mike Baker. From the link:
So with Clare, we have a New York connection, a San Francisco connection, and an actress connection.
The paper also mentions some of the other women in Chapin’s life at that point, including Sandy, who would become his wife, but none seems to fit the profile of “Sue” as well as Clare does. Lacking any other information, I’d make an educated guess that “Sue” is Clare MacIntyre.
I’ve got an idea that I heard Chapin, in an interview, mention that he read about the “actress” going through a divorce at about the time he was looking into the taxi licence. Sigh…my head’s full of old crap, none of which I’m sure is accurate, while I can’t remember to charge my cell phone.