Most soulful female vocalist

What female vocalist can sing soul like no other , and why .
LHasa De Sela. Only Soul of her left now, but I'm still enjoying her voice and songs. Ask Wiki for more info.
Joan Osbourne. Truly one of the most underappreciated female artists going. She has a voice that is one of the most beautiful, gale-force instruments I've ever heard in the pop idiom.
Don't know about the "most", but the Afro/Spanish singer Concha Buika deploys a smoky, sandpaper voice suffused with flamenco-like passion. Check out "La Nina De Fuego" and her collaboration with the great Cuban pianist Chucho Valdes "El Ultimo Trago".