She lived at the Pierpont Inn, where the family had been for generations, and which was about to be sold. Sam and Dean initially suspected Rose of trying to prevent the sale of the hotel by killing the people involved in the sale. The deaths were actually the fault of Rose's older sister, Maggie Thompson, who drowned at the hotel as a child and became a ghost haunting the hotel. Rose kept Maggie at bay for years with the hoodoo practices she learned from her nanny Marie, in particular Quincunx symbols.
When Rose suffered a stroke, she was paralyzed, and could no longer work the rituals necessary to protect her family. Maggie became Tyler's imaginary friend, and when Tyler was about to move away, Maggie tried to drown her, so that she would have the little girl with her forever. To save Tyler, Rose offered to die and serve as Maggie's companion, so the spirit would not be alone. Maggie freed Tyler, and Rose died. Her spirit became a little girl to forever play with her sister.