Teresa planned a bunch of murders, to avenge her mother's death.  She started on the visualize farm, because she needed a place to go.  Her father was an abusive alcoholic.  She left home, only to be drugged by the management of a visualize farm.  The guys start going crazy, getting violent.  She defends herself, and kills two members.  Teresa Lisbon  was the fourth member of visualize.  Stiles is keeping her secret.  She painted the smiley face to show that she was innocent; she killed in self defense.  The smiley face represents her happiness or peace of mind.