Karen Williams
Sarah's stepmother, and the biological mother of her little brother Toby.
Where is she from?
Sarah's stepmother is a minor character that appears in the beginning of 1986's Labyrinth, where she's played by Shelley Thompson. The name Karen actually doesn't come from any official source; she's named Irene in the universally rejected sequel comic Return to Labyrinth. The name Karen just seems to be something the fandom has collectively adopted, but inasmuch as GND is at this point far closer to being cannon, we're going to go ahead and call it official.
Comic Appearances
GND 063 - While Jadis tells horribly embarrassing stories about Jareth to Maleficent and Ursula, Sarah agrees to help him out, commenting that she's actually worse than Karen. Christine refrains from pointing out that they are the ones that brought her there in the first place.
GND 071 - Christine tries to sleep in, but is awoken when Sarah's brother Toby is dropped off by his parents Robert & Karen and he begins smashing about with Sir Didymus, Ludo & the Goblins.
GND 080 - With Robert & Karen coming to pick him up in an hour, Toby tears around outside on a tyrannosaurus with the Goblins, courtesy of Jareth's wish. Sarah, Christine, Erik, Javert & Crowley all watch with varying degrees of panic.