I believe Kristina Frye is Red John.
I'm afraid my biggest clue to that is not a very substantial one. You see, Kristina is the only "psychic" who was never exposed by Patrick. He never could prove or play her into giving her act away.
More, that thing about she "dying" and talking to him from the afterlife... Besides the fact that this is weird as hell, Jane also couldn't unmask her there. He always expose people's plays, but for the second time he couldn't do it to her. Her abilities matches his.
I also believe she has not one but many followers close to Jane, and most of them are the ones people believe to be RJ. In fact, I believe Brett Partridge is something like her right arm, and that´s why he can be identified in so many points of the story.
I believe Kristina might send him to do most things, like her puppet. I'm not sure if she does the kills herself of if she sends him to to the dirty work. She also manipulates others, but I think Brett is the most important follower she has.
Also, I believe Jane is about to start thinking that Brett is RJ, but he will find out he was just a puppet, like the guy he killed in the mall.
The other big things that make this possible:
- Listen to the limousine voice, looks feminine and also looks like her way of speaking: http://www.youtube.com/watch?v=pDqVYNtTso4
- When Jane is abducted, the guy in mask who sounds like Brett never disguised his voice, and also never said he was RJ. He talks about Kristina in the present, like she is still alive
- Gave information about Jane's daughter in the night of the murder
- The roll tide phrase
- The fact she went to TV to talk about RJ (so confident, because she know nothing was going to happen)
There are other small things that make sense:
- Painting toenails souns extremely feminine (maybe someone else do the killing and she finishes with that)?
- she just suddenly disappeared from the story
- Too much emphasis on talking about RJ as HIM or HE, maybe to cover up?
- she has red hair
- she plays a "psychic", like jane
- her indifference masked by her spiritualized life can easily cover for a sociopathy