I chose Carley because she seemed like a better friend for Lee than Doug, as she knows my secret but still trusts me and they both get along. Also another reason is because it evened out the male/female ratio in the group:
Male: Lee, Kenny, Larry, Duck
Female: Carley, Katjaa, Lilly, Clementine
So that is 4 males and 4 females. At the end of Episode 2 it is still even because Ben replaced Larry. Just seems like a good idea to have a mix, really.