I suspect there is more to the story.

First of all, why is she skateboarding from her dad's house to her mom's house at 7am on a school day?

And looking at her pictures, she seemed to have issues. I think at the least the family was very dysfunctional. Shit parents raising disturbed teens.

We don't know if it was "random" attack or not, only the people involved know, and one is dead.