Margaret wasn't running away to hide. She was a dead wizard walking. And she knew it. That much is in the text. As the how to safely meet someone who wants bad things for you, you meet them on the National Mall where they will be seen if they act.
Whatever Margaret knew it was valuable. Somebody was shielding her from Raith. Even if she was a deep cover agent of some type she still had to buy off her protector. Short of living her life in a circle, the only ones able to shield her that we are aware of were the Fae. The same way Morgan was shielded. And whoever did do it, did it for two years. Her stay alive card expired on October 31 when Harry was born.
That fact might lead you to believe that Harry was the price. Morgan isn't complaining that Harry was born. He bitching because Justin got in first. But there is another point implied. That Margaret had another thing so valuable it convinced Lea to protect her and then Harry. And this is pure speculation. Margaret knew who had the Atheme. Picture this, Lea doing a happy dance, and spending he next 25 years coming up with the price.
As an aside, the Senior Council knows about Outsiders. But that doesn't imply that they knew about Nemesis. But if the don't Cowl was right. And there is no reason to believe that the broader White Council is aware of Outsiders at all.
You missed my point. I'm just saying the Margaret LeFay/double agent scenario is a plausible explanation; at least for the present. Creating a scenario where Margaret LeFay sets a heavily populated public location as a meeting place with Morgan in order to curb his enthusiasm for taking quick and direct action is clever idea. However, something like that isn't a hinted at in the text. More importantly there are a few details it leaves out. How would she contact Morgan in the first place? Neither of them can use cell phones or email. OK, there's snail mail if Morgan kept a normal property somewhere, but Margaret would have to know that address. I'm sure you can think of some way she might send him a message, but how does she make sure no one else learns about it? Morgan might give his word that he would take no action until he heard what Margaret had to say, but that leaves everyone else on the White Council free to act and then there are her enemies to consider. Margaret and Morgan having a prearranged meeting place because they are already working together makes just as much sense. Again, at least in the absence of more complete information.
I didn't address Justin for a couple of reasons. First, because I didn't think there was anything interesting for me to say that wasn't already said by someone else. Well, maybe one thing, now that I think of it. (Though it's a minor thing really.) Both Ebenezer and Morgan despised Justin DuMorne. Ebenezer calls him, "that a son of a bitch DuMorne" and Morgan says "That bastard Justin DuMorne." In both cases what we aren't told is when Ebenezer and Morgan came to think of Justin in those terms. Because Jim has cleverly withheld pertinent information from us, it's possible both men only came to hate Justin after they discovered he had betrayed the Council and legally kidnapped Harry.
The second reason. I forgot what what it was. I'm sure it was nothing worth discussing anyway. I'll just add that Morgan not knowing what was more disturbing, Justin faking his own death or a 16 year old Harry actually killing Justin in a duel was a nice touch by Jim. I wonder if Jim put that in to get back at everyone who ever thought they were being clever by asking him if Justin was really dead, because Jim appeared to get really annoyed by that question being asked one too many times. I can see Jim saying to himself, "This will make them think they were right all along until I pull the rug out from under them when I do a real flashback scene and show that Harry really did flame broil Justin."
Finally, Justin having a magical way of transcribing a journal that Luccio web be likely to find. It's not a bad idea, but I wish there was something in any of the novels or short stories that were at least similar in nature to this. The closest is Harry's note to Ivy in Small Favor, but that doesn't work for Luccio. An old fashion physical dead letter drop that Luccio knew about might make more sense.