Joanne Harris is one of the pre-made NPC chefs in Downtown from The Sims 2: Nightlife. The other two pre-made chefs are Serdar Lewis and Calvin Ng. She usually can't be made playable without cheats, unless she is used as a walk-by on a community lot.
Joanne has the same facial structure as Margaret Howe. Her name is randomized when Downtown is generated. The name "Joanne Harris" is only referenced in the game files. According to her SimDNA in SimPE, her hair was black before it turned grey.