Becoming a Death Eater gave her an outlet to the darkness within her that she could no longer deny. If it helped her enemies, her former friends, to believe that she'd been brainwashed, so be it. She knew the truth. That was all that mattered. With each recovered memory, each fragment, Hermione was able to piece together parts of her past that she'd not been aware of for at least the past year or more. It wasn't always good.