When Casey is backed into a corner with her back against the wall, she'll throw her parents, George and Cindy, under the proverbial bus.
It will all go back to the events of Father's Day, June 15th. The last time Caylee was seen by anyone outside the immediate family was on that day, when Cindy took Caylee to visit her father in the assisted living facility, and a video of Caylee reading was made.
Casey will probably say that she took Caylee to visit her parents on Father's Day and her mother took Caylee to visit great-grandpa. Casey will probably say that when her mother brought Caylee home from visiting great grandpa at the assisted living facility, George, Cindy, and Casey argued about Casey's current living arrangement (living with Tony), and that she left in anger, leaving Caylee with her parents.
Casey will say that when she returned the next morning to pick up Caylee, that Caylee was gone. Her parents wouldn't tell her where Caylee was. She will say that her parents told her that she had one month to straighten out her life, and then they would talk about whether or not Casey would get Caylee back (Cindy's statement, "I've given you a month, I'm not giving you another day"). Casey will say that she made up that story about Zenaida to protect her parents involvement.
Casey's story about her parents being the last ones to have Caylee will fit the known evidence, including the hits by the cadaver dogs in the backyard of the Anthony home.