Warped Mirrors

Twilight takes a wrong turn looking for Canterlot High, and ends up in the middle of a war that has taken everypony she knows victim.

Twilight and Discord try to venture to Canterlot High, but winds up in a war-plagued Equestria, where nopony is safe, especially her. It becomes her task to bring the war to an end, and bring another world to peace.

This takes place before Twilght's Kingdom and Rainbow Rocks