I don't own Harry Potter.
It wasn't like one day she woke up and decided she was going to be what she was now. She wasn't born crazy or evil. She was born just like everyone else, or at the very least like every pureblood. She saw the world like it was, at first.
Then, slowly, she didn't. She saw it the way her parents wanted her to see it, the way it was easier to see. The world began to have a crack in it, a crack that let her see things the way she wanted them to be: pureblood and those that weren't pureblood. The mirror through which she saw life had a crack.
The crack that let her see the world as pureblood and not pureblood got bigger and bigger the more she grew until it wasn't just pureblood and not pureblood, it was proper pureblood and everyone else. She didn't notice the cracks. The mirror had always had cracks in it, for as long as she could remember it, and they were just the way it was.
Then the crack began to splinter, with more little cracks stemming out from it, distorting her view of the world even more, until it was proper pureblood and blood traitors and halfbloods and mudbloods and muggles.
She went to Hogwarts, and the cracks continued to grow. There was Slytherin and Ravenclaw and Hufflepuff and Gryffindor, and there were proper purebloods and blood traitors and half bloods and mudbloods and muggles. The mirror was cracking, but that was okay, because it was always cracking, letting her see that she was the best and everyone else was below her and those like her.
Slowly, she began to crack with the mirror. The cracks that let her see the world for what it was, no matter what anyone else said, began to crack her too. She was breaking down in her room and going off at anyone who didn't agree with her, but that was okay because she was a proper pureblood and just because the ones under her couldn't see the world with all the cracks didn't mean they weren't there.
She was breaking, cracking along with the mirror through which the world was reflected. She began to think that maybe, just maybe, her mirror wasn't supposed to be cracked, but then Mother told her about him. He knew the way the world was supposed to be.
She went to him, and he told her just what it was she wanted to hear, and she knew that he was one of the people who saw the world the way it was supposed to be. She followed his lead and did what he told her and devoted herself to him, because that way that looked right, among all the cracks.
She didn't regret it. The world was easier through the cracks. It was right with the cracks. Her mirror was cracked, and she didn't mind it one bit. But then again, maybe she was too cracked to care.