Maybe because she was sitting in a room with experienced law enforcement, and she'd done enough research online to know about Zenaida, but didn't want them to explicitly go after HER because when they did they'd find out she didn't take Caylee?
I don't think she meant to pin it on Zenaida; in my personal unprofessional opinion, it was never supposed to go down with them finding the car with Cindy tracking Casey down and calling the cops ... I think the plan was for law enforcement to think something sinister had gone down, and Zenaida was supposed to remain nameless.. she just based way too much of the character on someone real that she had looked up previously.