I know a girl that lives on the hill, she won't do it but her sister will.
Responses:
Old, Tired Spock
Illogical. Unless the sisters do not live in the same abode, which seems unlikely given the assumed source context, there are in fact two sisters who live on the hill, and the writer has knowledge of both of them, including the sister who "will do it."
Thus the inclusion of the other sister in the text is completely superfluous.
Old, Tired Kirk
Spock, if you launch into just one more tirade on Vulcan Dictates of Poetics I'm writing you out of my will.