I love a good linguistic mystery. I mean…this is one of those lines that is described as “much debated” which means that nobody is really sure what the heck it means.
I can see how you can make it mean something about the song. The song is the most likely candidate for the “it” in this sentence…which means we have to make wheel mean something to do with a song. Which…is massageable of course. A wheel, being something that rolls, could be a chorus, a refrain…in that it repeats and comes back around again and again.
And becoming in that context is enhancing , beautifying, etc. But further afield – becoming could be an active becoming – a transformative becoming – a wheel becomes something else. A wheel becomes…IT…whatever it might be. Maybe the song?
There is the wheel of fortune, which certainly is down, a-down, for her, at this point in the play.
I mean…there’s no knowing, for sure. Which is delightful. It also means that this line is usually cut. But hey…it is a delightful mystery just sitting there in the middle of a madwoman’s song.