You are a black Sirius and Regulus’ sister (regulus’ twin) whilst regulus joined the death eaters you and Sirius joined the order and we’ll also the death eaters . Voldemort sees you as a partner and his most loyal whilst the order see you as another soldier in the war. The death eaters respect you and the order see you as a pawn on a game of chess. You are practically playing both sides. The order don’t kill unless they need to and everyone thinks your innocent but you are not . You use your looks to get your way. whilst you are still in the order you don’t play by there rules. No one could explain the rapidly declining numbers in death eaters and certainly no one suspected her. Seducing the men death eaters with her good looks and taking them to bed before assassinating them. And regulus works beside her taking out the woman death eaters they are both wanting to end the war but on their own terms.