The truth is that I don't give a shit what she looks like, as long as she was the best actress for the job. Because if she is, then she will make the focus on what it should be when it comes to storytelling: the actual plot and development of the characters as the story progresses, instead of superficial things like "how similar she looks to the historical character."
If she was only chosen because she was black, then it sucks for the movie.