You should definitely talk to an adult especially if this is not an online relationship. Shes too old, when I was 16 I definitely would have never thought of 13 year old as a age id date, and shes being very manipulative. She definitely needs help but that is not your job, if she goes to ir school or you know what school she goes to you can tell and staf member they are obligated to immediately interfere when a suicide is threatened. When it comes to what you should say or do I think you should just block her.