In terms of performance, Wiig is cast as Barbara. Cheetah, on the other hand, will be 90% CGI, 10% stunt double(s), and 0% Wiig.
So its fair to say Wiig plays Barbara, but hard to say she plays Cheetah, apart from the voice acting.
So its fair to say Wiig plays Barbara, but hard to say she plays Cheetah, apart from the voice acting.