Twins?

My name is Isabelle Samantha Potter. I'm 15 and I am Harry Potter's twin sister. I never went to Hogwarts. Everyone thinks am dead. Even Dumbuldore. The night my Voldimort killed my parents and gave Harry and me our scars my aunt hid me from the world. She made me hide away from everyone. When I turned 15 the deatheaters killed her and stole me. Now everyone knows that I didn't die. Unfortunately their discovery was late because Voldimort got there first. I'll never join him. Now I need my brother to be here, to save me because I may be the 'dead' twin but I also am the key. I've got my own prophecy and it says that I will be the last holcrox not Harry. I will die that night for Harry to defeat Him. I am  very important. So how can we win if they find me too late? I am Isabelle Potter and I'm Voldimort's holcrox.