In my post-apocalyptic novel, the MC Eris navigates the world of survivors and grapples with her newly discovered abilities. The leader of the group of survivors, and the book's antagonist, Ezrith, had a wife named Saskia who was, unbeknownst to everyone, killed by Eris. I want to write a short story that centers around Ezrith and Saskia's death and how Ezrith handled it when it happened, but I don't really know where to begin.
Should I call my short story a prequel, or, since its a short story, can it not be called a prequel? Should I write my short story so that it could be read stand-alone, without previously reading my novel? And since the short story is written about the antagonist, whose backstory is tragic, how do I keep the reader from piling all their sympathy on her?