Spoilered since I'm talking about a pet peeve.
You know, I just hate that I have to reach across multiple media types to get the whole story. I might mind less if the comic books were worth reading or if I had someone to game with. It makes me feel just a little cheated. However it is his story and he has the right to tell it as he sees fit. Anyway.
Once you look it is obvious that Marling was somebody. Just off the cuff I don't make her as a practitioner, but I wouldn't place money on that. As someone posted earlier she uses a phone, but someone smarter than Harry may be able to shield a phone in some manner. In Proven Guilty Molly throws so much dust up with her magic that a subtle practitioner or a White could have been inside peoples heads stirring the pot and nobody would have ever known.
The story line kicks off before Dead Beat if I read the timeline correctly, possibly as early as Blood Rites. Kumori would have been busier then a long tailed cat in a room full of rocking chairs during that period. Marling would have been at it better than a year, both planning the convention and whatever time she spent in the halfway house. What I would surrender cash to know, was if Molly was serendipity, or the original target. It's almost like somebody was filtering troubled kids looking for talent. And hit the Jackpot with Molly.
Very subtly JB has made it clear that multiple people are looking for low level practitioners. Lara and the Fomor for example. And somebody knows how to find them. If I was gonna speculate I'd make Elaine a person of interest. A nasty suspicious mind would speculate that Elaine didn't dare reveal herself to the Wardens since they would want to Soulgaze her, that door is closed to Harry. That she is just the type of person who could get into knife fighting range with Harry given his proclivities. And she will know everything about the Paranet that Harry does after it's formed. She was close to the Summer Lady when she went pear shaped. And she could have been Nimfected by the Walker when Justin was killed. Quis custodiet ipsos custodes?(this was just too precious to pass up using)
As a closing thought on this subject, give some thought to a device like thorn manacles, but without all the sharp and pointy bits. With a potion, like JK Rowling's, Polyjuice potion. Remember that someone will use blood to accomplish something similar.