Jessie O'Brien was the wife of Frank O'Brien. She committed suicide in 1988.
Jessie worked with Luther Garland at the lumber mill and was one of the few people in his life that was kind to him. He developed a crush on her and expressed that fondness by drawing portraits of her.
Jessie was manic-depressive who in 1988, vanished after going off her medication. She was found two weeks later in a hotel room several towns over, the victim of suicide by hanging. Her husband Frank O'Brien, distraught over her disappearance, focused on Luther as the reason she was missing. Before he learned of Jessie's suicide, Frank descended on Luther at the mill and discovered him amid all of his portraits of her. Convinced that Luther had harmed her, he brutally chained him to his truck and hauled him up and down the mill road, killing him.
When Frank discovered the truth of Jessie's death, he was devastated even more so that he killed an innocent. Frank never faced any jail time as Al Britton covered up the murder.
The deaths of Frank O'Brien and two other healthy men from heart attacks brought the Winchesters to Rock Ridge to investigate. They eventually figured out that the men all died of ghost sickness, an affliction brought on by a buruburu, a ghost created from fear.
The boys learned that Jessie was cremated, and so ruled her out as the ghost they were looking for.