She was the first woman to include risqué material in her act. She wasn't "The Last of the Red Hot Mamas"... she was the first. She promoted and taught classes for young women who wanted to become Red Hot Mamas, too. Everything she did was original... she was one of the first jazz singers... certainly the first of the white jazz singers.
Of the many tributes to Billie Holiday's 100th birthday today (April 7), the most compelling I've heard is Cassandra Wilson's Sony Legacy album Coming Forth By Day, a strange, atmospheric brew produced by Nick Launay (whose credits include music by Nick Cave and Arcade Fire) with shimmering string arrangements by the incomparable Van Dyke Parks.