The 10th episode of season six hones in on why feuding sisters Carol and Barb ended up in prison to begin with. As it turns out, they originally had another little sister, Debbie, who was a ribbon dancing champion when they were in high school. Debbie's athletic career causes their family to uproot and move around constantly, so the two older sisters decide enough is enough — they take Debbie out one night, lock her in the car by herself, and then callously push said car into a half-frozen lake. The last we hear of Debbie is the sound of her terrified screams as she drowns.