Harry Potter fanfic. When Casedy 'Grayfelt' (fake last name from fake mother) Granger learns she was adopted she meets her real family and finds she has a twin sister all of this happens at age 10 right before her 11th birthday.
(Complete)
You're Draco Malfoy's twin sister. You're in your 5th year and are a transfer student. Draco is overprotective of you (even though he doesn't like to show it) and sometimes crosses the line. You're a baddie, but the real question is, are you like the rest of your family?