Problem1--there is no physical evidence to show how it was done.But she has killed somebody. There's got to be consequences for that. You can't just kill somebody and have nobody do anything about it, even if they were being mean to you at the prom.
Problem 2--She never made a verbal threat against him.
Problem 3--She made no physical move against him.
Problem 4--There is only that other guy that knows what she can do, but he has no physical hard proof to show otherwise.
Problem 5--Everyone there at that time, can be suspect, if it came down to it.
Problem 6--She is just a mess.