Actually, you're in the key of G, but starting on a C chord. But you're right, and,played that way, it could be a suspended fourth, but on the G chord, rather than on the Am7 chord.
There are a lot of different ways to harmonize this, and to think about the harmony. The sad thing here is that I don't think Marion is getting any closer to able to play this song, and won't be able to figure out what we are talking about til someone sits down and shows her.
Well, anyway, some of us are having a lot of fun with this song--