How many season 4 appearances are there by Mrs. Jennifer Knight?
CREATE TABLE "character_appearances" (
  "character" text,
  "played_by" text,
  "season_1" real,
  "season_2" real,
  "season_3" real,
  "season_4" real,
  "first_appearance" text
);
SELECT MIN("season_4") FROM "character_appearances" WHERE "character"='Mrs. Jennifer Knight';