The only info we have about it says that Maggie getting with Malcolm was her getting out of the plans and such she had with Lord Raith et al. Not that it was just another step in the plan.
He doesn't say she ended up loving him "in the end," just that she fell in love. I don't see anything in that description that would indicate that she met Malcolm for some ulterior motive -- Ebenezer clearly says she met him after running away from her former associates and, presumably, from the plans she had with them.
There seems to be this everpresent impression of Maggie Sr. of this ultimate planner that did everything completely purposefully and with foresight, but the evidence suggests she very much was not.
She was someone who slept with Lord Raith. On purpose. Multiple times.
If that alone doesn't spell, "Way too arrogant and really bad at predicting the outcomes of your actions," then nothing does.
As a rule, your master planners generally don't end up having to run away from damn near everyone on the planet that's aware of them for two years before being killed. That kind of thing happens to people who only think they're master planners.
This^^^.
I have never believed Margaret was this supergenius Xanatos-gambit-playing chessmistress. Nothing we know about her suggests anything of the sort, what we do know (including the testimony of her own 'shadow' to Harry) is that she was overconfident, arrogant, and in deep, deep over her head.
But I agree she probably did
think she was all that, at some stage. Remember when Harry was looking the painting of Margaret that Lord Raith made? It captured that attitude.
My guess, and this is all it is, but I strongly suspect, that Margaret was a particular type. She was very, very intelligent (which is not the same as smart or wise), very powerful, and probably mastered her magic early, and outraced her peers fairly quickly.
My guess is that she was cocky and arrogant and her failures, such as they were, were not such as to teach her humility. She was probably very, very clever...and cleverness is not necessarily a virtue. It can easily be a vice if not coupled to practical humility.
So you have a very powerful witch, with a long of knowledge, not much practical experience, very intelligent but not much first-hand knowledge of people, not many failures to haunt her, all ready to fix everything and go around the rules and so forth. Naturally, she rapidly got into deep trouble once she was out on her own.
I suspect she figured she could handle the supersex, so why not enjoy it? More than a few drug addicts have ruined their lives starting from exactly the same overconfidence. "I can handle it."
Harry inherited a little of that tendency, but he's smarter than his mother, and his life has pounded some humility into him along the way, too. But remember the incident with Chaunzoggoroth? Dealing with him was exactly the sort of thing I suspect Margaret used to do all the time, and like his mother, Harry was in over his head. By luck (or maybe a bit of help from Michael's Boss), Harry found out quickly what he was really dealing with, before it was too late.
Harry's also been learning in recent books a lesson Margaret didn't learn in time, Harry's beginning to realize that his elders often have good reason for their stuffy, annoying rules.
Regarding whether she actually had a Coin, I tend to doubt it. But she did, I suspect, get a chance to study the Denarians up close. For one thing, remember that shadow-copy of herself that she placed in Thomas and Harry somehow, triggered when they soulgazed (or maybe it was in the pentacles). It's not Lash, but it looks to me like something she might have learned to create by studying the Denarians, a baby version of Lash, sort of.
