I know it's probably unlikely but I just thought as I was reading the list - what if it is infact Juliet?
We know Kate won't go to the funeral, and it's perfectly understandable if it's Juliet, seeing as she watched her and Jack getting close on the island.
It'd also have an effect on Jack if another lady he fell for abandoned him. (divorce/getting in on with someone else.. dying?)
Juliet wanted to get off the island more than anything so what if she did (somehow) and then croaked it?
I don't know though obviously - just a random thought. =)