If #1 is correct, then we have the follow up question, why put a mysterious and random attempt to hurt Harry in PG rather than any other book? Here we have 3 possibilities - a) It was an attempt by someone who isn't normally in Chicago, so that was their only opportunity, b) it was specifically designed to try to keep Harry from interfering with the events in PG or c) PG is just as good as any other book for a random, mysterious accident and JB needed an excuse for Harry to talk to Murphy, so it was convenient to use in PG. Notably, it could also be any combination of any of the above.
I'd note that the car-bomb in WN is, i think, not confirmed as having anything to do with the plot of that book, so it's not impossible mysterious random killer strikes twice in two adjacent books.
With #2, we introduce a character whose level of knowledge of future events and ability to manipulate Harry and the future are at least equal to Uriel.
Indeed, we could be Occamian and suspect Uriel of that intervention.
It turns the entire themes of the Dresden Files on its head. Rather than being a story about Harry and free will, it's a story about godlike entities who can control everything Harry does.
Some of us believe it is already that to a large extent; that Harry's free will is all the more significant for being a thing he uses really rather infrequently.
And since they all have such perfect knowledge, it isn't even a chess game where one godlike entity might outmaneuver another, because they already know who will win in the end, so it is really just a complex math equation that only has a single proof.
Not to be too reductionist here, it is ultimately going to be a series of novels in linear text with only one endpoint, so there are levels at which I do not find that metaphor inapt.
At a telling-a-good-story level, given that Jim has explicitly introduced characters who have the degree of ability to out-think a human angels have, it would seem inconsistent and unconvincing to me for any that are interested in Haryy not to mostly be able to play him much better than he knows or can see coming.
From a Doylist perspective, it adds absolutely nothing to the story. Imagine this scene of events: Gatekeeper warns Harry, Harry drives home and prepares to use LC, just before he finishes using LC, the phone mysteriously rings. Tada, JB could tell the exact same story without ever using an accident. It would have the exact same outcome and provide the exact same mystery (why did the phone ring at that precise moment?). The only benefit JB would get from setting up a complicated superentity plan to delay Harry by the precise amount of time needed is that JB has an opportunity to have Murphy and Harry talk without relying on a "random accident."
OK, from a meta-story perspective ?
PG seems to me to be notably different from all the preceding books in terms of how standalone it is. A larger proportion of the significant players are people we've met before, and it's the first one where rather than there being a couple of loose ends, the ending is Harry explicitly acknowledging he doesn't have a clue about what was really going on at the centre of events. From an Aristotelian point of view, the eight book of planned twenty-plus-three is the transition between Beginning and Middle, and the differences I mention above fit with that. So if there was going to be a book for which "here is a random snippet of arc plot that could technically fit anywhere" was appropriate, PG seems like the best one to me.
That is a heck of a lot of knowledge for a guy that in TC, didn't even realize that Harry had claimed Demonreach as Sanctum and incorrectly predicting that Harry's plan would fail and cause more damage than good.
I'm inclined to think, considering how on-the-ball and well informed Rashid is in SK, that there's something specifically about Demonreach that is throwing him off in TC, rather than that TC is a reasonable standard for judging his degree of clued-in in general. And he has specified he will not set foot on the island.
You think she secretly helps Harry and covers his tracks so he won't be angry that she secretly helped him, thereby insuring that Harry gets the benefit of having the coin without ever realizing the benefits he is receiving?
Indeed. If the object of the exercise is to corrupt Harry's judgement without him knowing it - as witness the anger issues Murphy calls him on in WN, which are already showing in PG (where he concentrates on roasting the Giger-Alien fetch rather than stopping to help one of its victims, whom he then realises he might have been able to save if he'd acted differently). It fits that pattern.
Instead, she could avoid Harry's anger by providing help, forcing Harry to realize that with her help he can accomplish far more good (saving Molly) than he can without your help. Which is a better lesson for Lasciel "You need help from a mysterious source that wasn't me in order to accomplish your goals" or "I can help you accomplish your goals?"
The latter only works if she assumes Harry will be dispassionately rational about accepting her help, which he won't, because a) he has a pretty strong conviction that accepting help from Fallen will have long-term bad effects, and b) given a), Harry being Harry is going to be extreme ends of stubborn about it.