If Lash sabotaged Little Chicago / hid Harry's own mistake from him with the intent to blow it up in his face, why was she busting her ass to stop him from using it? Why would she want to kill the host she still had every expectation of turning?

I don't think Nic and co were monitoring her all that closely, or necessarily even had the capacity to give Lash orders remotely. The Shadow is sort of a fire-and-forget weapon. Harry picked it up; he'll convert eventually - that was considered a 100% certainty until Harry showed he'd resisted in SmF. Nic didn't see a need to micromanage. He'd got some intel of Harry using Hellfire, and figured it was just a waiting game from then on.

Based on Lash' willingness to go to extremes to stop Harry using the table, I wonder if she'd even noticed the flaw but was for some reason forbidden from telling him it was there. She seemed awfully sure he was about to kill himself trying.

The problem with LC being broken has always been the question of  why Butcher chose to write it as broken and then only do the reveal in the denouement?

Lash's reaction only makes sense if she believed LC was broken.  And if it were sabotaged she was the only one able to do so in plain sight.

By the time they are actually in the lab for first use the plot has essentially failed.  Michael is in position.  Harry now knows what is what and who is who. LC has been fixed and the only task still on the table is to get Molly and  be shown what has happened at Arctis Tor.

Butcher having Harry pick up the coin was the perfect setup for this.  In terms of the plot this  may have always been the point.

It was all about saving Harry, Rashid was buying time until Micheal got to the meeting.  Michael says as much if I remember correctly his arrival wasn't about saving Molly, but Harry.

What he actually said was this.

“Only that it is entirely possible, Harry Dresden, that this entire affair, beginning to end, is meant to protect you. That when I went to the aid of Luccio and her trainees, I did so not to free Molly, but to prevent you from coming to blows with the Council. That her position as your new apprentice had less to do with protecting her than it did protecting you?”

If you follow the reasoning that Butcher has used to keep Uriel  from wiping the floor then you  should ask why he could involve himself. The only reason that makes sense is that somebody crossed the line.

I have found the last piece of the puzzle for my personal head canon for Proven Guilty.  This shouldn't be confused with the truth, whatever that is. I still have no idea of who fixed LC.

There appear to be two murder plots running concurrently in the text. There is the obvious one.  The Merlin being manipulated into trying to kill Harry once again.  This is probably the WC traitor (Peabody) stirring the pot. Magic ink and all that.

Then there is the  second plot. The one by the Denarian's, possibly/probably  in concert with the Black Council. This one is trying to either get Harry to pick up the coin or to kill him if he uses LC, by having it blow up in his face.

This second plot is inferred rather than explicit. This is tenuous but the reasoning is thus. Lash shows up two times in the book, unless I'm forgetting one. She appears just before the crash and she appears just before first use. She is the only one who could have blocked Harry or Bob from seeing the flaw in LC. If Nicodemus is to be believed she could have controlled Harry and told Bob to not see it.  Harry never would have known.  Her active intervention let Uriel put his thumb on the scale.

Why didn't Rashid just tell Harry what Molly had done.  They had to empty the basement so someone could get in and fix Little Chicago.  In addition Mab had to show Harry the attack on Arctis Tor so Harry could answer the first question that Eb asked. Why didn't Mab declare war on the Red's?  Thus answering the question, why did Mab have Molly brought to  Arctis Tor?

For my personal fan service and head canon this is good enough.  It ties up most of the loose ends.

I hope I don't get moderated for too long a quote, but here goes.

“Indeed, child,” she said. “Did you not think it strange that in your turmoil-strewn time here none of your foes—not one—ever sought to enter from the other side? Never sent a spirit given form directly into your bed, your shower, your refrigerator? Never poured a basket of asps into your closet so that they sought refuge in your shoes, your boots, the pockets of your clothing?” She shook her head. “Sweet, sweet child. Had you walked much farther, you would have seen the mound of bones of all the things that have attempted to reach you, and which I have destroyed.”

“Yeah, well. I nearly wound up there myself.”

“La,” she said, smiling. “My guardians were created to attack any intruder—including one that looked like you. We couldn’t have some clever shapeshifter slipping by, now, could we?” She sighed. “You took a terrible toll on my primroses. Honestly, child, there are elements other than fire, you know. You really ought to diversify. Now I have two gaping maws to feed instead of one.”

“I’ll . . . be more careful next time,” I said.

“I should appreciate such a thing.” She studied me quietly. “It has been true for your entire lifetime, child. I have followed you in the spirit world. Created guardians and defenses ’pon the other side to ward your sleep, to stand sentinel over your home. And you still have only the beginnings of an idea of how many have tried.” She smiled, showing her delicately pointed canine teeth again. “Tried, and failed.”

Which also explained how she was always near at hand whenever I had entered the Nevernever. How she would be upon my trail in seconds whenever I went in.

Because she had been there, protecting me.

I have no idea what the deal was between Lea and Margaret but as of Changes it was still in effect.

I frowned. “But . . . you sold my debt to Mab.”

“Precisely. At an excellent price, I might add. So now, all that remains twixt thou and I is your mother’s bargain. Unless you would prefer to enter another compact, of course . . .”

This is Lea speaking to Harry about the Garden on the other side from Harry's lab where the Primrose Path and the caterpillar live. The one she used to guard that portal.

Uriel couldn't protect Molly since she was a victim of her own choices.  He was involved obliquely because of a more direct action by someone else.

Mab's involvement was a product of having Lea on ice. She was protecting Harry. Which of course is what the whole book is about.

The Korean is brought to Chicago to get Harry in the mood to climb on his murder bus. That's what all that puking and retching is about.

Yes, I thought it was foresight. And Rashid didn't tell Harry about the specifics (even if he knew), in order to not disturb the upcoming events leading to Harry entering Arctis Tor. Also I think it was about Harry learning stuff and making choices with certain powers (including the Gatekeeper) not allowed to tell him directly and not to be involved directly. Their involvement would need to be balanced and so on. This would complicate things too much.

... and also there would've  been a lot less books needed to tell the story. 

I like that last line.  A lot of truth there. However if foresight was involved the question would be foresight about what? By the time the letter reaches Harry Molly has already done the dirty.  But you come by the idea honestly, Butcher feeds it to you, implying that nothing has happened yet.

“Meaning that it’s possible nothing has happened, yet. But that he wanted to put you on your guard against something that’s coming in the immediate future.”

Since you know Molly had already done Black Magic the question is foresight about what?

However this digression doesn't really speak to g33k's point about Mab.

Honestly, that could have been just "random" bad luck.  Not *everything* has to be part of the Grand Conspiracy.  Given how prevalent marijuana is in high-school, the odds that somebody is carrying -- in a car-full of teens -- is awfully high.

But that provided an opportunity, I think, that was ruthlessly exploited... or, as you suggest, it could also have had a little nudging from the Spooky Side.

I don't think we have *nearly* enough info on Molly's magical training/education before Proven Guilty.  There's nothing to indicate that anyone in particular was (or was not) involved.  Mab could have been... Titania could have been... Ancient Mai could have been...  <shrugs>  Or it could have been 100% mortal stuff by low-level practitioners and wannabe's and untalented booksellers &c, without any push from any of the Supernatural side of things.

My bet is on Mab (possibly via one or more proxies).  I think she was "nudged" toward mind-magic (and fear) specifically to get "on the same wavelength" with the phobophages, Mab's personal cadre of Fetches.

Too many elements "came together" in PG for me to think Mab wasn't manipulating Molly from long-before the beginning of that volume.

The events in the book were set up about the time that Cowl was getting his puppy ass kicked in Dead Beat. Madrigal was invited a year in advance. Molly was popped at about the same time.  This is also the point when Lea is imprisoned. Molly only commits Black Magic two weeks before  after being prompted by Sandra Marling to use fear. Mab could have done it. All that requires if for Butcher to want it to be that way. But if it was Mab manipulating Molly why go through the other events?