But frankly, I think Bianca was too low-level to be told about Nemesis, and the true nature of the curse on the blade. She just knew it as the Athame of Morgana LeFey, an incredibly-potent magical implement; that's enough for Bianca (it was enough for Lea, when she realized she had Morgana's Athame). Nemesis was still hidden. Remember: Ferrovax himself was there, and almost certainly would have taken exception to Nemesis or any other Outsider-influence (WoJ puts the Great Dragons as part of fine-tuning the world -- on the level of raising mountain ranges etc -- which puts them pretty firmly into the anti-Outsider camp).
You could be right about Bianca, but then again as my brother in law says, "she is just smart enough to be stupid." If Cowl or some other agent of Nemesis was able to convince her that to enable the infection of Winter, why wouldn't she go for it? I doubt that she would have thought it through. Lets not forget this is the woman who fed upon her beloved secretary until she died and then blamed Harry for it because he pissed her off.
As for Ferrofax, I doubt that he'd care one way or the other about what the lessor beings around him were doing, or Nemesis. He demonstrated that in Peace Talks, he has his own selfish reasons for doing what he does, and at Bianca's party he was there only for the gold.
I don't doubt Lea was planning on getting something from Bianca; but she may have been open to any roughly-equal-exchange (bringing the Sword entitled her to receive a very strong gift in return! (recall that Winter Law requires Lea to expect this (or exact retribution); the Ramps will know this, and even blind-with-ambition-Bianca would think twice about earning the enmity of the Leanansidhe)), or Lea may have had something else in mind, some item from Bianca's treasury. I think the cues in that scene suggest that Lea was a bit surprised -- and more than a little pleased -- at what she got.
You gotta look at the context, what Lea said pages before the party.. Even if she was surprised by Bianca's gift, it doesn't change her pleasure.. Why? Because it brought her power, not for her Queen, but for her.. Also interesting that when she did give it up, she gave it to Maeve, her Lady, not Mab, her Queen.. Hmmm... Do I smell a conspiracy that backfired because neither realized the Knife was infected?
But fear is an intense motivator, a great lever to move someone to action.
And Mab is a master at manipulation; and Lea is Mab's Handmaiden...
Yes, but no connection to Harry trying to kill Lea with a Holy Sword, then losing it to her because of that.. Which set off events that actually made things worse for Winter. Not Mab's style.
Nemesis is incredibly hard to detect; I don't think Mab knew the hidden peril at Bianca's court.
Hell, I don't think Bianca herself understood it; she was a pawn on the board of much stronger players, playing a much deeper game.
As I said, Bianca was just smart enough to be stupid, and she was the pawn that ultimately led to the total check mate/end game for the Red Court.
More than "a bit," I think! 
But note that Mab likes her that way; it's probably a major component of why she picked Lea as her "handmaiden." Lea & her ambition is a key part of Mab's own regimen to keep herself at the top of her game.
With in reason, there are lines that Mab won't allow to be crossed. Lea knew that, I think when she realized she was infected she confessed to Mab and pleaded for both a cure and forgiveness.. However she didn't apparently confess to giving the Knife over to Maeve in time for Mab to cure her as well. That, or Maeve was much more vulnerable to the infection than Lea was.
