exceptional voices of female singers (non-classical)

It would help if I read MORE carefully before posting an emotional response!

Tablejockey, FWIW there were others who have also posted in the thread expressing surprise that a particular artist had not been mentioned earlier in the thread, when in fact the artist had been mentioned earlier in the thread.

BTW, there’s no need to necessarily read more thoroughly. Just use the "Find" function of your browser to search for a given name, on each page of the thread. I often find that function to be very useful.  In Firefox and Edge the Find function is in one of the sub-menus which can be accessed under the three bars or three dots at the upper right corner of the screen. It will also be under the Edit menu, at least in Firefox, if the menu bar has been enabled at the top.

On another note, also FWIW but relevant to the OP’s question, a quote from Sir Elton John:

Judith Durham, like Karen Carpenter and Eva Cassidy, possesses the purest voice in popular music.

Regards,
-- Al

Thanks very much, John (Roxy54). Here are some videos of Judith Durham with The Seekers, which provide about as good an indication of the quality of her voice as one is likely to find in a YouTube video of a 1960s recording:

"The Carnival Is Over" (composed for them by Tom Springfield, Dusty’s brother, who wrote a lot of their hits):
https://www.youtube.com/watch?v=-5G1OkFLQPY

"Someday, One Day" (composed for them by Paul Simon):
https://www.youtube.com/watch?v=yiIqhY5-SKY

"Love Is Kind, Love Is Wine" (composed by Bruce Woodley, the guitarist on Judith's right):
https://www.youtube.com/watch?v=_VAAMueQQYk

Best regards,
-- Al

Given that the question focuses exclusively on "the instrument," and excludes repertoire etc., I'll add Connie Francis to my previous suggestion of Judith Durham.

Best regards,
-- Al

Based on the purity and sheer beauty of her voice, I would cite Judith Durham, best known as the lead singer of The Seekers although she has had a distinguished solo career as well.

Following is a brief excerpt of comments about her provided by a British gentleman whose bio is shown at the end of an article he wrote entitled Judith Durham: The Voice of the 20th Century. Obviously some of what he has to say in this paragraph and in the rest of the article is debatable, as well as being subjective to a considerable extent, but his comments are not without foundation IMO.

Judith Durham (of the Seekers) is the greatest of them all. The voice of the twentieth century, in my not very humble opinion. Clarity, spine-shivering (I’ve already used “spine-tingling” and I’m all for a bit of variety), astonishing purity – all that is obvious straightaway. But listen to The Carnival is Over or the amazing Just a Closer Walk and you hear a vocal beauty which is unique and reaches a level no one else can get near to. Callas is just a tear-jerker by comparison; Carpenter just a female crooner; Piaf just a screeching Gallic banshee. Judith Durham combines a bold, even brash, confidence in her own ability with a deeper humility which lends her remarkable sound an even more profound character.

Best regards,
-- Al