This seems like a rather minor part of a conversation Carlos had with Harry, at Marcone's Castle before Ehniu showed up.
Carlos - "How's Karrin doing?"
Harry - "Like always, but slower and grouchier."
Carlos - "I heard what she did. Went hand to hand with Nicodemus Archleone and survived."
How did Carlos or anyone from the White Council know about this? Was someone sitting under a veil watching the whole thing play out? That seems highly unlikely. I don't think Rashid saw it through some time travel message shenanigan's. If he had it's unlikely he would have told anybody else unless he believed it was necessary to do so.
I'm going to eliminate Nicodemus and the Genoskwa from the list of people who would have spilled the story. One's on the run and the other would rather kill a human than talk to one. That leaves Harry, Murphy, Michael and Waldo Butters. Charity was in the safe room with the children.
Murphy was pretending that her injuries occurred in a traffic accident and Harry would have backed her up on this. That leaves Michael and Waldo and Michael was in the game a long time before that day. Long enough to know there are some things you don't share around the campfire.
I think Waldo Butters shared the story of Murphy going up against Nicodemus with some of the people on the paranet. He wouldn't have done it out of maliciousness, just a lack of understanding that some things need to be kept under wraps. Unless, it was Mr. Sunshine and that seems really, really unlikely. Do you have a different solution?
A couple of other questions come to mind. Shouldn't Harry have been surprised by Carlos' question? If Ramirez knows about Murphy going against Nicodemus, how much more does he; and the White Council, know about the break in of Marcone's vault? For that matter, what about the rest of the major players in the supernatural world. For example, shouldn't Lara know the same facts? However, even though Carlos knew that Nicodemus had been set up, he gave Marcone all the credit for doing so, which was incorrect. Marcone and Hades provided the bait. Mab was the real brains behind the plan and Harry made it happen. Do you think Carlos realized that Harry was involved, because it didn't seem like he did to me? If you want to reread this passage, it's in chapter 25, page 238.