This is a fascinating thread. While I may not believe all of it there is circumstantial evidence of a remote possibility.
Stevie was there briefly before rehab. This was one song she recorded then.
Lindsey was a crafty SOB on Tango. Everyone was asking who the female grunting was until he spilled the beans it was Lindsey speeding up his voice.
Stevie was absent during most of if not all of the Tango in the night sessions. We learn that even if Mick's first book even Christine lashed out at Stevie for not being there when Stevie complained about not having involvement with the album.
I think its a very real possibility Lindsey's vocals were added to the song when Stevie was not there. They needed her songs and she was not there.
Last piece of evidence is the Oooh my love from the Tango sessions. OMG I never heard a more out of it Stevie. She is singing like she is bored to death. It her worst singing demo ever. It could be the intense pressure on Lindsey to complete the project and not start over with Stevie drama. I totally believe Stevie drank heavily before singing in the Tango sessions. Just listen to Oooh my love. She sounds out of it and drunk.
Remember the band is not going to talk about what sad shape Stevie was in during 1986. We just get bits and pieces. This could be another piece. Maybe an exaggeration but I don't think totally out of the realm of possibilities. Now I am curious and need to listen to WISYA really close. From the first time I heard the song I thought all the wassa matter babies were a bit odd and too much. Even the Rolling Stone review of the album which was mostly positive made fun of that part.
GOSH, can you imagine the book Lindsey could write if he wanted to tell the truth.