I really enjoyed that dynamic between Betty Buckley and James in Split, [and wanted a] very, very intelligent woman challenging the precepts of these men, and what they believe in, and trying to help them in some way.
It just suddenly felt right, that, wow, it should be a female character challenging these guys in a therapy session.
I originally was sketching [the character] and I was like, Gosh, should this be a man or a woman?
I had two different actors in mind and one was male and one was female, and obviously Sarah was the female choice.