First off, the lighter is most likely to smoke pot. I can't imagine a lighter being involved in her grisly fascination with serial killers and brutal drawings.
I don't know about the rest. There are a LOT of people interested in true crime, and who want grisly, grisly details although they usually couch it in insincere concern "horror! I hope we don't find out she's been murdered! I don't think I can stand another sad outcome of a missing person!". Check out internet true crime discussion boards to see what I mean.
I think you should talk to her about it. She'll be angry you looked, but what she's drawing and interested in goes beyond a typical interest.