So they call Mae "Nova" when they believed her to be just this feral human incapable of thought. Fun fact, an actual nova steals material from its companion star—much how Mae stole from Noa more than once in the film for survival.
And a supernova is an explosion that happens when a star dies. The aftermath of its death is crucial for the formation of new stars and planets, for the evolution of the universe as a whole. (Mae's mission is crucial for the perseverance of her kind)