Black Hanakawa did seem to know (or at least guess) that Shinobu was in Araragi's shadow. She specifically had him stand where the shadow was strongest and seemed pleased with the outcome.
Fun fact: When Bakemonogatari was originally broadcast, it ended at episode 12, the date with Senjougahara. Obviously, those of us watching it weekly were a bit confused that the whole cat plotline had seemingly been dropped. The last three episodes released online a few months later.