I remember reading a commentary (documentary?) on this where Roger Waters (or someone from PF) told her just to wing it and she was pretty insecure about the end result. Knowing it is an impromptu extemporaneous composition reflects highly on her talents and she certainly deserves credit for her role in making this one of the best pieces of music out there!
At the time she did it, she was pretty delighted that they liked it so much; but I suspect after time and talking with people about what she had done (and the fact that this song has become a classic and made a great bit of money) it made sense to get a bigger slice of the pie. A shame that the band (I like to think it is the manager/lawyer that is the asshole) didn't acknowledge her contribution when she contacted them more recently!
Does anyone know? Did she tour with them for concerts?
The actual foundation of the song is a little fuzzy for me, but her part is crystal clear in my mind!