I am going to try very hard to remember those names for later, but forgive me if I ask them again. Also, I am holding you to that promise of a cookie.
So, if I'm understanding this correctly, the dragon god, Ceiphied, fought Shabranigdo the dark lord, but couldn't defeat him and so both of them got cut up into little bite sized pieces and scattered all over your world and your sister just happens to have one of them. Is that why she's insane? Or is it the power that's making her crazy?