I think they would have a marginally better chance if they tried to say Casey was a victim of abuse ,depression,momentary reality break,or it happened during a blackout of which she has no memeory ect.
Or the time worn "It was like I was in a fog y'know?...watching someone else in a movie..." routine.
If they try to stick with the Nanny story and claim Casey has no involvement the prosecution is going to tear them apart.
Her lawyers must know this.
I have a feeling her they will use the chloroform use as a sex drug and that can really mess up your mind. RM may be the center of this, his using it on KC and that fried her brain. I don't buy it, but maybe jurors will.