You were a powerful witch. Being the leader of an urban ledgened all the way from the time of just God and his children. You're magic saved you as a baby, your body unable to fight your fathers demon blood coursing through your veins after a miracle of him and your mother creating you. Without your magic, the demon blood would kill you since it wasn't a small infection like Sam's.
But, after Cas opened the gate of purgatory and held every Leviathan inside his body, the infection Cas carried ended up touching your magic, infecting it. The black marks spread down your arm everytime you attempted to use it. Without knowing, the infection was killing off your magic, making you prown to powerless. And without it, you'd die. The only way to cure yourself was to kill their leader, Dick Roman.
Bobby, Sam, and your best friend Mayven all left the room after discovering the news, leaving just Dean and you. You couldn't believe the news. It felt like your whole world was crumbling at your feet.
The room was full of heavy sorrow and worry as no one knew what to do. Without your magic they were down a power against the Levithans and saving Cas.
"Hey," Dean pulled your attention away from your overwhelming mind, pulling you into reality. "Everything it going to be okay."
Except, it wasn't.