So, I have enjoyed the many thoughtful posts in this thread. It has led me to another question. I don't have a theory yet, but wanted to post it to allow others to add it to the questions here.
If the WoJ is that Mab is as powerful as stated, then why did she the attack on Arctus Tor to continue? It seems to me that given the location that she could have shown up and pretty much crushed any attacking force. Which leads me to ask, why do we think Winter was defending? If Mab was distracted, Maeve could have been in control of Arctus Tor and that the battle was an attempt to retake it.
I see one of two possibilities for this coupled with Maeve being in control of the forces at that time...possibly her failure hinted to Mab that something was seriously wrong with her. But either theory requires Mab to be 'indisposed'.
Option 1: Mab was AT the Outer Gates. We know from Rashid that certain years the battling is more intense than others. The Red Court's decimating of the Council forces coupled with their 'invasion' of Fae territory in the NeverNever was both done with the help of them calling up Outsiders. What if a subsequent or parallel push was made at the Gates themselves, enough that Mab HAD to step in even if just briefly. This is either a plan to get her away from Arctis Tor to attack it, OR they are just opportunistic enough to take advantage while she is gone and Maeve is probably in charge with Lea incapacitated.
Option 2: Mab was busy curing Lea. This is admittedly the weaker of the two choices because we still don't have nearly enough information regarding Nemesis, how it infects, and what it takes to rid a person of their influence. But supposing for a moment that it requires someone more or less of Mab's power to eradicate it thoroughly from the system, that could take some working...maybe she has to slip into Lea's consciousness and actively burn Nemesis away. As she is busy at work, enemy forces are at the gate ready to strike because Maeve has informed them she is in charge while Mab sees to Lea.
Either way I think overall Maeve WAS in control of the forces at Arctis Tor for some reason or another. Whether Mab is at the Gates or in Lea's head she could still be aware of what is going on around her, (hence the statue wink), but could not pull away from one of those tasks because doing so would mean she lost something...either a pivotal battle, or her right hand woman.