talk about a landmine girl
I think this is a red herring and she only did this because the other party failed to kill Meguru, and wanted to murder suicide in case they succeeded in the next attempt. I swear I've seen this trope before in other murder mysteries.
That being said, the observation that Hinami's small frame makes her too weak to kill with a knife is hilariously wrong withhow much effort it would take to incapacitate Meguru and move her body around.