Castiel: angel, brother, soldier, friend, protector

Background

You're a 15 year old girl. You're an angel just like your older brother, Castiel( who is the definition of an overprotective big brother) , however you're a different kind of angel. A very very powerful one. More powerful than the arc angels. When you were born, all the other angels wanted you dead because they were afraid you would be too dangerous with so much power. Castiel thought otherwise and believed that you had a lot potential. So, Castiel sent you down to earth, in hopes you'd be safe there. While on earth, John and Mary Winchester adopt you( being unaware that you're an angel) and take care of you, along with their two boys, Sam and Dean. After Mary's death John taught you and your adoptive brothers how to hunt. John ended up getting killed by a demon and ever since then it's just been you and the boys. ( I forgot to mention that you have no idea you're an angel either)