How is Queen Jadis selfish?

In The Magician's Nephew, Queen Jadis's selfish nature is first seen upon meeting and speaking with Digory and Polly. In chapter 4, Digory and Polly happen upon a world where they find a room of people who seem to be frozen in time. After Digory rings a bell, Jadis, one of the frozen figures, approaches Polly and Digory. She soon reveals that "her people" are frozen because of something she did. Jadis was in a battle with her sister. As Jadis's sister was about to win, Jadis spoke the "Deplorable Word." Jadis knew that if this word was spoken it would "destroy all living things except for the one who spoke it" (p. 66, The Magician's Nephew). Even so, she would rather rule as queen of a world with nobody in it, than not rule at all. If she allowed her sister to win, everyone would still be alive, but Jadis would not have the throne.
When Digory announced his concern for all the people she had destroyed, Queen Jadis showed no remorse or concern for anyone but herself, simply stating, "What else were they there for but to do my will?" (p. 67, The Magician's Nephew)