Boohyah
I found the Topic that jman101 was referring to. It's probably the best original theory posted in the past year or so IMO.
I see - so this idea was originally Knnn's? Well, whoever first came up with it - kudos to you - I think it's great - it explains so much and it all hangs together.
Other things also click in place to support Knnn's theory - the link with the homeless shelter, Molly originally going to meet Crane. None of this did I pick up when I read it, but once it's pointed out - it all makes sense and it's really clear.
I also like Knnn's idea of Molly being an Outsider-bane. Yet another reason the BC would want her. And why they'd go to any lengths to stop her becoming WC.
A corollary of this theory would be that the Gatekeeper, while he might have his own agenda in all this, can't be a part of the BC. If he was, he never would have warned Harry there was black magic in Chicago. Maybe he's not Grey Council, but in his own way he's opposing the BC too.
One more thought - someone in that thread you quoted asked why Mab would have sent all her troops to Summer's borders if she thought BC were planning to attack Arctis Tor. IMO Mab wanted to know who her enemies were. The BC has always been rather anonymous/nebulous - working in the shadows. I think Mab wanted to put faces to them so she'd know exactly who to destroy. So she took something they really wanted [Molly] and sent her army away to entice the BC [or at least some of them] to come out in the open for once. It worked to some extent - we know one of the Denarians showed up - he must be one of the major players. And know she'll know who he is.
I dont think this gamble was as dangerous as it might at first appear. Others have pointed out - [1] Arctis Tor was her home and the seat of her power - very unlikely any enemy would have the power to defeat her there and [2] she could have recalled her army in a flash if it proved necessary [which apparently it didnt].
I just love this theory - it explains so much. So Knnn - take a bow!