IIRC in the Casey Anthony case they had to prove first degree .....No other choices for the jury. All or nothing.
Remember several discussions about Florida law must state lesser degrees to convict of lesser degrees. You may want to check that.
Goodness you couldn’t be more wrong RE: Casey Anthony. There were different charges the jury could have chosen other than 1st degree murder including 2nd degree murder, aggravated child abuse, or Aggravated manslaughter of a child. They chose nothing except lying to the police.