two cents accepted
and your change is...
whatever (probvably mortal) wizard was the firsts idhe by definition was not fey; much as the erlking, 'her' much much younger peer was not originally a goblin.
at the time winter first noticed molly, she was not Harry's apprentice, in fact if they had not noticed her it is likely she might not have ever become harry's apprentice. If you go by Lea, Molly was still a kid when winter noticed her.
and Mab could, if given the lawfull opportunity, steamroll eb, injun joe, and the merlin, while driving a yugo, backwards, and eating a ham sammich at the same time.
as to harry's friends being the trigger, you have a plausible concept, but JB has stated that he will quite likely (ie, you think Mab hasnt heard that excuse before?) still be winter knight after GS. so if eb did do it, boy did he screw up.
we have these facts:
at some point, Harry will either time travel or cause someone to time travel.
He shall deeply regret bonding with demonreach
the isle, and its darkness, predate the last ice age.
it
may have something to do with the sidhe table. The logic is unporoven, but highly plausible.
Mab knows crap that is explaiable only by divine foresight or absolute foreknoweldge.
Mab
may have manipulated harry ionto taking demonreach, again, it explains a lot.
Mab
may be in love with Harry
Molly is the focus of Proven Guilty...
now by all means, counter with annother scenario.