When I want black, I go with (of course) Aretha, Ruth Brown, and Irma Thomas. I gotta admit though, Annie Lennox’s vocals on "Would I Lie To You" is about as good as can be expected of a white UK woman ;-) . I love the song; even Blondie drummer Clem Burke (not a favorite of mine) sounds good on it. Great use of brass (horns), too.
One real fine white female Blues singer is Lou Ann Barton. Her debut album was produced by the great Jerry Wexler (and Glen Frey!?), Aretha’s Atlantic Records producer. Lou Ann sometimes tours with Jimmy Vaughan. She’s the real deal.
Dan Hicks had two female singers in his Hot Licks band, one being the wonderful Maryann Price. Her vocal on the Johnny Mercer classic "I’m An Old Cowhand (From The Rio Grande)" is one of my all-time favorites. It’s found on Dan’s Striking It Rich album, produced by Tommy Lipuma. Fantastic album!