I’m still not getting how we’ve gotten to Mab is fighting an Nfection - her actions from PG onward seem to be effective against Nemesis at every turn, & I don’t sense any conflict in her - her biggest conflict from books 7-14 were how to deal with the Nfection in Maeve. I thought there was a tragic symmetry in her being able to save Lea, one of her best “friends” but not Maeve, her own daughter.
While I do believe that there is some credence to the theories that Lea is not completely healed yet, I am yet to see any evidence that Mab is Nfection or fighting off an Nfection personally.
If she suspected that Lea had been Nfected (which she obviously did), why would she handle the athame so carelessly? After all, it’s an object of such power that Amoracchius is considered a replacement.
Personally, I think that if Mab is Nfected (which I'm not sure about) then it comes from imprisoning Lea in Winter's Wellspring. Winter's Wellspring would seem to be the heart of Mab's power, so it makes sense to me that, along with allowing her to cure Lea, having a Nemesis agent literally in the heart of her power would put her at some risk for Nfection.
Obviously, Mab would not have attempted to cure Lea if she thought that it would result in being Nfected herself, but she may have underestimated Nemesis.
If Mab is Nfected, she's obviously fighting it effectively for the moment, but that probably won't last. I tend to think of Nfection as something like tuberculosis, in that it can/will go dormant when the host is strong, only to emerge when the host weakens. If this is the case and Mab is indeed Nfected, then as things get worse (as they must, given that we have an apocalyptic trilogy coming up) Mab will become vulnerable and Nemesis will strike.