Life was simple for Narcissa as a child. She was innocent, cute, and very clever. She caught on to everything rather easily, and was a natural observer. Because she preferred observance to participation, she was stamped off as dull from a young age, never being seen for the clever young woman she was. She took on all of her mother's lessons quickly, though, learning from a young age how to be the perfect lady for her future husband. Not that marriage was ever too interesting to Narcissa, but she knew better than to defy her mother and become looked down upon. Her comfort at home depended on her parent's seeing her in a good light. And that worked well for a long while, until she was about fourteen.
Her marks in school were perfection, she took as many classes as she could, and she excelled in them, her best being Potions. Her father was thrilled that his daughter was so intelligent, but her mother had other ideas. She believed that women should be refined, pretty, and vapid. Intelligence only got in the way of proper behavior, and that wouldn't do. Plus, Narcissa was starting to fill out and gain curves. Soon she would grow bigger as well. No, no, that wasn't proper. Skinnier was better, and she made that clear to Narcissa. She made it a point to point out when she gained a pound, or if her dress was a bit too tight, that she was a gross disappointment. Narcissa soon began to believe her, and she began eating less and less, until she was eating just about nothing. The little she did eat was immediately purged from her body, lest she retain the fat in it.
That went on for years until Lucius Malfoy took note, and was absolutely disheartened that such a beautiful woman was doing such a thing to herself. He helped her through it, day by day, step by step, until she was eating normally and not shaking to throw it all up. The process kept her constantly around him, talking to him, getting to know him, and she soon realized that she was falling madly in love with the Malfoy heir. It turns out he was feeling the same way, and nothing had made her happier that to be with him. Even her mother approved, and they wed a year after she graduated (with top marks in all her N.E.W.T. classes.) She was blissful, and so happy to actually feel happy.
But, as it would happen, all the abuse her body had suffered for years made conceiving very difficult. Between the stress of trying to conveice and the stress of her husband running around every night risking her life, it took them eight years to actually have Draco. They had tried so many times, suffering three miscarriages and one stillborn before their beautiful son was finally born, and she pledged she would do absolutely anything to keep him safe. Even if she had to sacrifice herself. It was only a year and some months after his birth that The Dark Lord was defeated, and she felt like a weight had been lifted. She now had her husband at home with her, no longer risking his life, even if they were helping everyone keep out of prison. She didn't mind that at all, though. These were her friends and she was going to do everything in her power to keep them safe as well.