I'm pretty sure that the moment her temper cracked, and she made Harry bleed, was not the moment she realized Maeve's Nemfection; the moment she said "It was the knife" to Harry was not Mab's realization/recognition that it was the knife.
It's okay, we can agree to disagree, I am just as sure that you mis-read and misunderstood what you read.
Mab's response in Cold Days was not a denial of any of Harry's suppositions about what was making her so angry back in Small Favor..
When she responded, "it was the knife." It was her confirmation that what he was saying was right.
Pretty clear, easily outlined..
1] Lea receives unknowingly infected knife of power in Grave Peril.
2] Not sure that was the book, but I believe in Summer Knight there is one scene where Mab has that same knife in her belt..
3] At Arctis Tor we find crazy Lea on ice and silent Mab on ice, both had contact with the knife, one or both of them are infested with the adversary in Proven Guilty, and taking the cure..
4] We have the really pissed off Mab moment, ears bleed and eyelashes freeze, in the chapel of the hospital in Small Favor...
5]
Most significant point, after Maeve's death in Cold Days, Harry pointedly asks Mab about
that very scene in the chapel in Small Favor, linking what he thinks Mab realized in the chapel, to the execution of her infected daughter, Cold Days..
Jim doesn't do that randomly, bringing up a scene from three books before. Linking that scene to the aftermath of Maeve's death,
Jim was underscoring the point! Harry confronts Mab about that scene,
"That was why, Because you figured out that the adversary had taken Maeve, And it hurt." So in essence, he is asking her a question and answering it at the same time.. "So that's why you were so pissed off.."
6] Mab has no argument, no denial, "it was the knife.." The infected knife began it all, introducing the adversary, taking out Maeve, and bringing in Molly as the new Winter Lady..