No, imo, not a problem. Every one does not have to agree exactly how or why a crime happened. There are always going to be some unknowns in a crime.
What they have to agree upon is that Casey was responsible for her child's death. If 8 people think she was poisoned by chloroform, and 4 think she was duct taped to death---that is fine. They can legally and ethically vote Gulity.
What every one has to agree on is that the defendant deserves to do time as a punishment for a specific crime, and then how much. Our justice system is based upon plea deals and negotiating for higher or lower charges and punishments. So juries can do the same type of negotiations and they do--they deliberate. If I was on the jury and I wanted the DP, but nobody else did, I would be forced to cooperate and compromise, to avoid a hung jury.
The only way a jury would hang is if at least one person was absolutely convinced she was innocent of all charges. But if some think it was an accident, involving negligence, and others think it was murder 1, there is nothing wrong with coming to a compromise. imoo
The way I look at it, if it was 100% accidental, then she brought this on all by herself by the ugly, vicious way she acted. [ accusing others, blaming her friends/family, having people search and donate.] I would have no problem with her serving jail time for the things she did in the horrid aftermath.