XD me neither.
Solve this riddle and you could be a psychopath!

Timeline as I see it:
The mother dies of some random reason (not murder)
The funeral happens
the girl meets a guy she likes and they date
the girl doesn't get the guy's number so they have no way of communicating
the sister gets murdered.

idk how there is a connection and reasonable linear path in that but ok, im saying mine sounds correct due to the time line of how i explain it and how if you think just the right amount you'll understand

The girl herself was her sister's killer. She was desperate to meet that guy again.
Ok now i get why Crystal said whoever solves it may be a psychopath
Figures. Now if you'll excuse me, I need to rub some mustard on my nipples again.
ye the girl killed her sister hoping the mystery man would attend her funeral

According to the FBI, if you can solve this riddle, you could be a psychopath!! - A girl is at her mother's funeral who died unexpectedly. But she met a guy at the funeral she didn't know and they INSTANLY hit it off. She got busy receiving condolences from the guests and wasn't able to get his phone number before he left. Following the funeral she tried really hard to track him down, but no one knew who he was or how to contact him. Only adding to her trouble, a few days later her sister was found dead. The police suspected it to be a murder..... Who did it and why did they do it?
the girl kill everyone from grief
I think the girl did if it was her sister. But yeah...I'm not psychopath