Someone maniacally telling another to commit suicide is not abnormal. High school students are the greatest culprits, as they are immature yet are capable of great jealousy and hate for others. In a situation of low interaction, or one that imparts little feeling of repercussion, making such statements becomes easier for some. The best example is on the internet, yet low interaction situations like texting might also be times someone would be more likely to say such a thing.
A common conversion involving some anger and depressive thoughts might lead to something like, [person 1]: "Maybe I should just kill myself". [Person 2]: "No, that's exactly what you should do". [Person 1]: "Oh, just shut up". [Person 2]: "No really, you should kill yourself".
This kind of bullying is not uncommon, yet actually having knowledge of a person midway through the act and still encouraging the suicide is a different story entirely. My only explanation is that this girl harbored some jealousy or anger for the boy (who she clearly had some form of interaction with in the past as they had each other's cell phone numbers) and thought she was in no danger of being accused for the act. Obviously phone records trump the intellect of a high schooler.
