When she first saw Lucius Malfoy, the only word that would come to mind was 'ice'. Everything from his pale coloring down to his haughty demeanor suggested a coldness. The look of contempt and disgust he gave her froze her inside while, at the same time, it made her burn to change the world so that men like him could no longer look at her like that.
Years later, meeting him in dark alleyways where he'd give her information in exchange for a rough and dirty go against the side of a building, she still sees the ice in his eyes. Contrary to what he believes, she does realize that he would be giving her the information without the sex. However, she goes along with it because she loves knowing that the bigoted bastard can't stop himself from touching her. She's not the reason he turned spy, and she really doesn't care why he did, but she's the reason that there's a fire burning out of control beneath the ever-thinning layer of ice.
She wanted to change the world, but it changed her. It would have torn her up when she was younger, but now she's content knowing that it changed Malfoy as well. The world is as it is, and it will change in its own time, bending only to a person's will when it sees fit. Those rules apply to pale-colored, haughty Death Eaters as strictly as they apply to rebels, saviors, and know-it-alls.