An interesting--and ominous--footnote to her work on the song:
"She had a miscarriage upon returning home from recording Gimme Shelter; some hypothesize this was due to the strain associated with reaching such high notes whilst singing." Source: Snowden, Don (March 13, 1986). "For Clayton, The Gloom Is Gone". Los Angeles Times.
At any rate, because The Stones market their shows to a mainstream, rather than hardcore, audience, special guests in concert would have to be generally well known.