I think she wanted to kill whoever ate the lunch then kill herself, with the idea that if they die around the same time then even if they don't know each other they'll at least meet in the afterlife and it won't be as lonely. My best guess, anyway.
@SonicDisgaea98 There are low job offers and low worker offers. Maybe it isnt easy to substitute her... our maybe this is a crazy island full of demonic, sadistic and crazy people......................... what do you think?