I don't think I have a phone buzzing power anyway.
I care because she is, or at least was, your friend and I can see this ending very badly which will end with you feeling hurt and I don't want that.
The city has no Champion. All it has now is the Chosen. How a Slayer is made the Chosen warrior of the Powers is a complicated business, one that I partially understand, but the short version is, with no Champion, the responsibility falls to her as the longest serving Chosen One. In every generation a Slayer is born. One girl in all the world. Powerful words.
Have you spoken to her yet about how her thought processes went? Do you know if she had questions, doubts over her choices and herself? And really, has your sister stabbed her in the back?
[ooc: Cas promises this isn't down to mind control!]