The main thing we know is who her likely associates were. It is an interesting list.
Nicodemus - says he respected her.
Not just respected, he says he has
'fond' memories of her. Think about that.
Now, he could be lying (he does that), but there is one piece of supporting evidence for a connection between Margaret and the Denarians: she planted something in the minds of her sons that looks suspiciously like a baby-version of a 'shadow'. One place she could have learned about that sort of thing, and studied how to do it, would be with the Denarians.
The message-Margaret in their heads was far short of Lash, but it was still an impressive bit of magic. I consider it evidence for a Margaret/Denarian link.
Justin DuMorne - mentioned as an associate by Ebenezar.
Goodman Grey - calls her a piece of work.
Leanansidhe - mentioned throughout the series.
Also, note what Lea tells Harry in
Grave Peril. Lea is trying to comprehend why Harry would risk a painful death in order to do what he was doing, and she has trouble fully comprehending his answer. She does, however, note that his mother sounded the same way...just before her death. What Harry has been throughout his adult life, his mother apparently found just before the end, a change from what had gone before.
Ebenezar - says the Wardens were under orders to arrest, and he had orders about her as well. Why send the Blackstaff after a lone wizard?
Note that Ebenezar
specifically tells Harry that Margaret had violated the First Law, along with others. Not 'pushed the edges' or anything, but straight-up violations of the Seven Laws.
Now, her killing with magic might have been self-defense, in itself. The Council would probably not have looked favorably on even that, given her other associations.
(The Council is far more likely to accept a self-defense claim in a First Law violation if that Wizard in question had not gone out of her way to get into situations where it might happen.)
But she had also violated other Laws, and Eb also tells Harry that she had deliberately used the Council's Laws as weapons against the Council. It doesn't sound like her actions were easily defensible.
Thomas Raith - calls her "one hell of a dangerous witch".
Chauncy - says she was headed for Hell, "but we lost her".
The above list suggests Margaret LeFae was involved in very shady business. She had also broken at least some of the Laws of Magic.
Which is where things get strange and contradictory.
Yeah, we have all that. It's pretty consistent. But we also have the very, very
strange conversation between Harry and Stacy in
Dead Beat, the one that implies that she was just a misguided idealist.
Rashid is also said to have had an occasional dinner date with her, where they discussed Faerie and how to traverse it. Of course that could have been further back, before she went majorly bad.
But something happened to make her change her ways just before the end, apparently something pretty profound. Whether it was meeting Malcolm, or whether she met Malcolm as a result of it, or just what, we can't know. Insufficient data.
As for Thomas...this is really nasty. Thomas believed that Lord Raith had her addicted to White Vampire sexual ecstasy, and that she broke away. Lash told Harry something that chimes with that, adding that she found the strength to break away 'for a reason' involving the birth of Harry as a starborn. But it's not clear if she
knew that, that is, if her desire to produce a starborn gave her the strength to break away, or she was given the strength to break away because of her role in some larger cosmic plan.
Why didn't she take Thomas with her? We can't answer that, because we don't know the circumstances of her 'escape'. It might be that the opportunity presented itself and it was 'then or never'. It might be something else. There are a lot of unanswered questions about that whole business.
Thomas told Harry he thought their relationship started out as business, and turned personal. What Eb told Harry about the infamous 'dinner party' years later chimes with that, but it doesn't explain how she got addicted.
Even her being addicted is odd. I mean, as an experienced Wizard, she presumably ought to know better. "Here, just one done of the heroin..."
Of course sometimes supposedly smart people do profoundly stupid things,
especially if they pride themselves on how smart they are. Which brings us back to what the shadow-Margaret told Harry, that she was 'so arrogant'. Harry saw a look of arrogance in her portrait at Chateau Raith, too.
Was she arrogant enough to think she could enjoy supersex without getting hooked? I don't rule it out. Still, it's another case of 'insufficient data'.