I have decided that my mind is going. And everybody but me probably has realized this. But on my umpteenth reread of Proven Guilty it just occurred to me that Sandra Marling is the prime mover. She triggers all the events of the book.
She knows who Molly is. She plants the idea that traps Molly into Black Magic by suggesting that fear can control addiction. All the young people who Molly was associating with have her as a common denominator.
Molly looked at me obliquely for a second and then said, “She’s a part-time volunteer at one of the shelters where I’m doing community service. She helped Nelson out when he was younger. Rosie too, and her boyfriend.“
As the convention Chair she would have known that Madrigal Wraith was on the agenda. She would have known the theater owner and the location of his theater. She's at the hotel when all the events happen. She leads Harry to Molly so he can get her away from the police and allow her go home where she was vulnerable.
She is described as middle aged and while there is no description of her height, there is this.
“Mister Dresden!” called a voice from across the crowded convention hallway. I looked up to see Sandra Marling hurrying through the crowd toward me. The convention’s chairwoman looked exhausted and too nervous to be awake, much less standing, much less politely pushing her way through a crowd, but she did it anyway. She still wore the same black T-shirt with the red SplatterCon!!! logo on it, presumably the same I’d seen her in the night before.
“Ms. Marling,” I said, nodding to her as she approached. “Good afternoon.”
For Harry to see her in a crowd and identify her she would need to be tall enough to be seen. That's a stretch, but humor me.
Last, but not least, myrk or something like it is used in the attack and will be used again later in Small Favor under similar conditions by whoever sent the Hobs. As well as a ward.
My WAG is Kumori. But that is purely a WAG.
It also occurred to me that she was a ghoul posing as a human with Maeve doing the magic is the background. Again a bad WAG.