Feels weird saying you gotta let go of revenge for the sake of the victim. But its also true that she's the one making fumika suffer by bearing the grudge and turning it on other people
Probably due to conflict or self destruction due to human greed. She saw the only way to preserve a system that would always arrive at that point is to have a reset button.
I know its probably story convinence but as much as it seems necessary to kill to protect themselves the humans always seem to relish in killing animals when they have any advantage. Definitely contributes to the perpetuation of violence.