Rosalind Harker is a former lover and ex-girlfriend of Red John, believed by her as a mysterious business man called Roy Tagliaferro.
She is a blind and solitary young woman (described by Patrick Jane as a "lonely soul") who had a relationship with Red John, who called himself by the alias "Roy Tagliaferro". According to her, his car broke down near her home in the small county of San Angelo, and he spent the next few months in a relationship with her. He liked listening to her playing the piano, especially Bach. He left her without saying goodbye, though he did draw one of his trademark smiley faces on a wall in her house (which she herself couldn't see, being blind).
In "Red John's Footsteps", Jane and Lisbon found her and got a description of Red John. Though Patrick saw the smiley face on the wall, he didn't tell Rosalind that she had been in a relationship with a serial killer.
In the end of "Little Red Book", Patrick contacted Rosalind and called her to a morgue where the body of Timothy Carter, one of Red John's associates who had manipulated Patrick into killing him by pretending to be Red John himself, was kept. He had her feel Carter's face in case she could identify him. She told him that she had never met the man before, confirming Patrick's suspicions that Red John is still alive.
She returns again in "Red Is The New Black" in which she tells Susan Darcy the man that Jane killed was not Red John, who pays her a visit the following night. He listens to her play the piano like before, holding a white teacup and sitting on a lounge chair, but by the time the authorities arrive he has fled, leaving Rosalind apparently hypnotized and with the dead body of a morgue attendant in her closet. She is in witness protection ever since. In Green Thumb, her name was seen on a fake list of Blake Association members (which is odd, since she has no known connection to law enforcement).