Sadly her attorney is right from a defence prospective. What is the first thing an attorney will tell a client (guilty OR innocent)> DO NOT SAY A WORD!
At this point even if Casey said IT WAS AN ACCIDENT - DO YOU HONESTLY BELIEVE LE WILL NOT GO AFTER 1ST DEGREE MURDER? Even if she told them that at the beginning they woul STILL have pursued a 1st degree murder case against her.
Look at what they did to Cindy Summer. Look at Darlie Router. Sorry but as sad as this is, you must listen to your attorney and keep quiet until or unless you can get LE to agree to pursue a charge that fits the facts. Good luck with that!