Most Helpful Girl
Well does she display any psychopathic tendencies or thoughts? I mean we all do have some but when you have most or all of them then you are probably a psychopath. And you can follow the homicidal trade which is bed wetting (not as a baby but older when they shouldn't be doing it), fire setting (purposely not accidently) and hurting/killing small animals (most serial killers start killing animals before moving to humans).
If she displays none of this signs then she probably isn't a serial killer.
Most Helpful Guy
If she wets the bed, kills animals for fun and likes to start fires then chances are she's a serial killer in the making.