Fragility
Disclaimer: I don't own Death Note.
She was no idiot, no matter what anyone else said (or would say).
As soon as she had met Yagami Light, she had known that he would end up using her (like a toy) and discarding her (like a piece of trash).
She knew that he would overlook her own intelligence and opinions (couldn't she think for herself, for once?) and fill her with his ideas (he'd regret that).
She knew that he would eventually kill her (she would be a virtual fountain of his secrets by then, too precious to let live), and she would go to her grave smiling (the others would pass it off as a tragic accident—they were all too common nowadays).
She knew he would never, ever trust her (despite his promises).
She knew that he would never, ever love her (how she longed to whip off her wedding ring and throw it in his face).
She hated him with every fiber of her being, but she still stayed with him (he was an anchor, not a love).
She knew she shouldn't cling to him (she still did, out of necessity).
She knew that in the end, she was just a broken tool (well, at least she knew that he was worse than a broken tool—he was a dead fool!).
No, she was anything but an idiot (she was just a lonely doll, beautiful in her fragility).