She has a particularly striking appearance, whether one finds her attractive or not, and she is recognized as a talented actress. With that combination, how can one not wonder at casting her in an apparently minor role obscured by CGI?
'Hot off her Oscar win, beautiful talented actress earns herself a bit part as a CGI alien in the upcoming Star Wars movie'...doesn't work for me on the surface. It's not like Star Wars needed a star presence in a small role.
Maybe the role is really cool and maybe well served by her voice and physicality. I certainly hope her casting wasn't about her race. Though I appreciate Bingo's concern as there is a record of casting non-whites in alien parts.
I agree with SilverWook that there is a good chance she, like Serkis, would have a second role.