Technically, it IS in the film and you can hear it if you've got the bonus disc set of Dreamgirls on either DVD or Bluray.
Anika's screen-test is of her singing 'Ain't No Party' and she just kills it. She's fantastic as usual and shows why she was the only one in the film who insisted on doing all of her singing LIVE. No click-tracks for this girl.
Besides, anyone who saw her perform on the Oscars last year knows that she had the most talent on that stage (of the three). The notes she was hitting were incredible. Even JHud can't do that.
I love me some Anika