I do not believe that Casey will receive the DP, although she probably deserves it. However, I am glad they put the bar that high because it gives them more wriggle room. If the highest penalty was LIFE, then she would likely receive a little less. This way they aim for DP, but jury may settle for LWOP and feel that was merciful.
I agree that they need a lot of alternates. In a high profile case like this you can lose 2 or 3 jurors in one fell swoop if a family member taints one of them on a Sunday visit by telling them something sensitive, and then they pass it on.