Angelic But Demonic

This is a City of Bones/Mortal Instruments fanfiction.
Crystal seems like an ordinary girl at first, but when she kills a Demon and leaves a witness behind, her whole world changes. After running away from the house she grew up in, not far from a certain Vampire(Simon Lewis), in Brooklyn, New York. Crystal finds her way to the Institute and barely gets away from what she was running from. Before she can even explain whats going on, she falls unconscious. When she wakes up she meets the residents of the Institute and finally finds out something she thought she would never truly know what happened.
What will happen when Crystal faces the person who made her run away in the first place? Will she defeat that person that everybody wants dead? Will she ever return home without a curse on her shoulders?
You'll just have to read to find out!
((This is a X Sebastian fanfiction) This does not turn into a lovey-dovey story! Nore is it to make Sebastian seem like a good person.)