Draco Malfoy's mother is not the most loveable creature around. But there's something very human and moving about her love for her son and her plea to Snape to take care of him. She implores Snape in Chapter 2, "Severus – oh, Severus – you would help him? Would you look after him, see he comes to no harm?" (2.150). It is Narcissa who compels Snape to make the Unbreakable Vow, the likes of which connects Snape to her son's life and mission, forcing him to do everything in his power to keep Draco alive.
But then again, we see her mean side when, at Madam Malkin's, Harry encounters her and Draco. She lets her warts show: "I see that being Dumbledore's favorite has given you a false sense of security, Harry Potter. But Dumbledore won't always be there to protect you" (6.67). And then she REALLY lets her warts show: "'You're right, Draco,' said Narcissa, with a contemptuous glance at Hermione, 'now I know the kind of scum that shops here….We'll do better at Twilfitt and Tatting's'" (6.77).