I know, her failure to provide any phone numbers, address, etc, for the nanny is very incriminating against her. That plus the failure to report was why all the suspicion landed on her in the first place, after all.
JG asks the question about "who was really watching Caylee" in one of his interviews, which can be linked to from the "interviews" sticky. I don't remember if it was after he had gotten together with the Anthonys and a couple of the friends in that initial effort to figure out a timeline, or how he arrived at that question. I'll have to read it again.
Also, Cindy asked her in the jailhouse conversation, "Is Zannie the one with the apartment that has drums in it, in the photos we have? " apparently implying, 'is Zannie actually someone at Ricardo's apartment', (or maybe she meant another friend who had drums, seemed to be implying RM apartment.) KC at first agrees, yes, that is Zannie's apartment in the photos with the drumset. But then when Cindy keeps pressing she finally says, well, that is Ricardo's apartment you're talking about, but Zannie also has drums and her apartment is 'set up the same way'.)
Of course some people theorize that "Zannie" was actually any friend KC left Caylee with here and there. Some people even theorize that Zannie could be an alter-ego of Casey, i.e. Casey herself. I honestly don't know.