Naaa. I think it was Casey replying to her mother telling her they wanted to talk to her. There have been many discussions about what she was saying.
IMO, she said something like __ ___ ____ talk to them. (Maybe "I don't want to talk to them?")
eta: Or, another one speculated on was "why do they want to talk to me?"
When I heard that tape originally I was sure that she had said something snarky (in spoiled brat mode) back to Cindy about not wanting to talk to the police. Then Cindy hands her the phone and says, "Here, talk to them".
ETA Listening to it again, it does sound like she either says "I'll never get to talk to them" or possibly "I'll never get the trunk clean". Maybe she was complaining to Lee that the reason she couldn't talk to the 911 dispatcher was that Cindy was "all over it" and not going to let her get a word in edgewise. Sadly, I could see either statement coming from her!!