Leah Potter: Found at Last (A Harry Potter FanFiction)

Set during Harry Potter and the Order of the Phoenix., Leah Jacobs (Potter), 15, has lived at an orphanage all her life. When a mysterious and slightly scary woman, Bellatrix Lestrange, comes to "adopt" her, Leah is less than thrilled. She discovers magic and is found at last by the magical world. And it's a far more serious than she had ever believed.

PS> This is under the assumption that Bellatrix Lestrange escaped from Azkaban before the rest of the death eaters that had broken out, and it has been hushed up... :P