You know, I think actually the Anthony's knew about this accusation before Caylee even died. I just read the FBI's Nick Savage depo, who references mother- daughter jealousy and sexual accusations. I think this accusation is what Casey is refering to in the jail visit when she says "don't worry, I haven't said anything". I think this is what Lee is refering to when he asks "is this like the last time?". I think either there was sexual abuse going on in that home, or because Casey is borderline personality disorder, she was claiming sexual abuse as the ultimate topper as a wedge between her parents, as an excuse to steal from her family, as a reason to be out of control and not be responsible. And I DO think the defense is going to intimate that the family believed, or wondered, if GA was the father of Caylee.
But none of it matter, except maybe in mitigation. She doesn't get to kill her baby, no matter how abused she was or wasn't.