Edit:
Alternate Theory:
“Whoever called up these phages,” I said, “needed a way to guide them from the Nevernever to the physical world. They needed a beacon, someone who would resonate with a sympathetic vibe. Someone who, like the phages, wanted to make people feel fear.”
Butcher, Jim (2007-02-06). Proven Guilty (The Dresden Files, Book (p. 270). Penguin Group. Kindle Edition.
Lea sent the phages after Molly. We know from as early as
Grave Peril that Lea wants Molly; she asks Michael Carpenter for his eldest child. She's high up in Winter and might reasonably be able to command fetches, as Mab's handmaiden and highest servitor.
The "Attack" on Arctis Tor was actually Lea with the Athame (and the Black Council?) attempting to rebel against Mab. Sure, that happened at least more than a year before (prior to Dead Beat, since Lea's imprisoned then) , but what's time in the NeverNever? Mab conquered the attack all on her ownsome, so no probs.
Of course this theory has the problem that Lea was imprisoned at the time, but perhaps she'd given standing orders to the fetches?
Hrm. Perhaps Lea had a standing bargain or deal of some kind that forced Mab to send the fetches.
Yes. But she's just making sure Harry pays his debt. Not kidnapping someone to force him to take more. I feel that if Mab was in the business of kidnapping people to get new debt, the WC woud try to stop her. Now you may say that she's too strong. In fact I'm sure that an alliance between the WC and Summer would be devastating for Winter.
Yeah, but the WC isn't going to rush to defend a budding warlock ! That just makes it fit even more! Molly's no longer an innocent, so nobody's going to defend her .. . except Harry. Or, well, her dad, and his cold iron magic supersword, so maybe this wasn't a perfect plan on her part after all . . . or maybe she planned on trading for the Sword. . .