I think the ending for the author and cliff was alright, but why is that girl with the sho...

I think the ending for the author and cliff was alright, but why is that girl with the short hair so obsessed to see them suffer? As if she doesn't want to see herself with a new life but rather stay there to see them, people she hated, suffer? I think it's a better choice to be able to live her life a new since she's already punished them