I'm hearing parts at the end of this that may have been used in the final recording. The vocals are pretty exact, even how she's singing the lines. I remember thinking this years ago when I heard these alternate versions. Basically, from 3:48 on sounds like the vocal on the album. The only difference is that in the album version she goes from "of our love affair" to "like a whip through the air" which is missing from this version. So, it sounds to me like they've taken sections here and there and kinda pieced it together. You know this band likes to do things like that!

And yes, her vocal (although I wouldn't call it dreadful), does sound like she was in the middle of doing her taxes or eating french toast when they whisked her away to do a vocal.