Exotic vocal

Ms. Haza did not appear on the Physical Graffiti album. She did a cover of the song. The only woman to have ever shared a mic with Robert Plant on an album was Sandy Denny on the song "Battle of Evermore" and what a voice she had!

Lene Lovich. She sounds like she's from Mars.

I won't post it here and it is mostly male singing, but try Mongolian throat singing on youtube, there is a lot of that there. Quite unique.

Little Jimmy Scott
Exotic? Yes. Female? Not really, but you be the judge....

https://www.youtube.com/watch?v=dDei1D72XAQ

https://www.youtube.com/watch?v=JtqGpgdD_6k

https://www.washingtonpost.com/entertainment/music/jimmy-scott-hard-luck-singer-with-a-haunting-voice-dies-at-88/2014/06/13/270725b6-48c3-11e3-a196-3544a03c2351_story.html

Throat singing? Tuvan throat singing??
Try Paul Pena in Genghis Blues. Pena, by the way, wrote the Steve Miller hit, Jet Airliner.
Not female, of course.

https://www.youtube.com/watch?v=itrN11AwNMo

Surprised no one has yet mentioned Bjork.  

Hey many still to mention...
Not only Bjork, but I believe Sinead O'Connor uses throat singing as well.