Emmet died and the truth died with him. Mandy has never been so popular, but getting Emmet to kill and killing Chloe had never been about that. It hadn't been about revenge that no one noticed her until she was beautiful or bullied her.
Mandy just wanted to see if she could have that power over someone, she Emmet. At least for a while. She wasn't sad he was dead.
After all, he wanted to die. Things had worked out for them both, Mandy thought as she began to write a novel based on what happened. Her version of events.