Except there's an arc to the show itself, which is, basically, that she's preparing to die.
I think the subtlest, most devastating aspect of Audra's performance is that she is so attuned to the development of Billie Holiday's development as an artist and as a human being is what she does with her voice.
At the beginning of the show, Audra's voice is Billie circa 1947: more seasoned and mature than the piping, sweet voice of 1930s Billie singing with Teddy Wilson and Count Basie and Artie Shaw and Benny Goodman.
But as the 90 minutes goes by, her voice gets more ragged, as Billie's did after her arrests for heroin, as the drugs and alcohol took their toll on her body, spirit, voice and soul.
By the end of the show, Audra is singing the way Billie did at the end of her life, as you can hear on her final recordings with Ray Ellis and as you can see on her 1957 television appearance on The Sound of Jazz with Lester Young.
It's a subtle choice on Audra's part, noticeable only if you've listened to enough Billie to know the difference between the sound of her voice in the different periods. But for the average audience member, it devastatingly dramatizes her decline.