Also a jailed Thomas may eventually talk, a dead one won't. They need the why ... especially after the Titan invasion. It happened way too soon after this to be dismissed as coincidence. And the svartalf spies in the White Court have probably told them that after Harry threw Thomas in jail Lara was very pissed at him.  And if they could get an account, possibly by Freydis, from Vadderung's organization, Lara, with her Valkyrie bodyguard, attacked Dresden for this - and were swatted down like flies.

Are there svartalf spies in the White Court?  They don't exactly blend in.  Even if there are, they're not eavesdropping on what happened at Demonreach.  The island's intellectus would have alerted him to other people on the island.

I think the Mantle is unalterable.  Meaning that Nemesis couldn't latch on to it.  So It's connection was lost when Maeve died. 

I think that Mab knows that there is too much humanity left in Molly.  She needs Molly to give herself to the Mantle, completely.  A Winter Lady that's conflicted is tolerable, a Winter Queen is not.  The Queen must be laser focused on the mission at hand.  The mission to protect the Out Gates at any cost. 

Remember that Molly loves Harry.  Mab does not.  She see's Harry as a weapon, and my guess is a disposable weapon that isn't supposed to survive past the Stars and Stones.  Molly might not have what it takes to sacrifice Harry the same way Mab will do it without hesitation.

Mantles are alterable, likely not by Nemesis, but snipping off pieces of power and trading them along and melding them with other mantles happens (e.g. doing that is probably the main purpose of the Stone Table in Tir Na Nog).  Taking on the santa mantle let Odin go from his original perception to the one we think of today, but it's a slow process.

I agree that Mab thinks Molly has too much soul to be a proper Winter Queen.  She's too emotional to take up Mab's mantle in her eyes.

She became worth it the moment she became kine for the immediate Raith family..  Big clue here, she's insane, but feeding on her makes her sane?

I'm sure there are dozens of them at any given time.  Papa Raith liked to surround himself with them as bodyguards before BR.  Why not porn star Bobby that Inari fell in love with too?  He'd be the boyfriend of Harry's brother's sister.  Maybe Nemesis's plan to install him as the Merlin's personal butler just hasn't come to fruition yet.

But Maeve was infected, not possessed apparently.. As far as that goes, Maeve never had a "handle" as you call it on Harry, but Thomas did as of Grave Peril.

Maeve is important completely independently of Harry.  The Winter Lady is a great target to wreak havoc on the balance of reality.  A mortal Raith girlfriend is not if that's the best credentials she's got.

Nemesis has the time...  All that time it has someone on the inside, watching.. Hence the name HE WHO WALKS BESIDE, that is someone that goes along, they don't interfere they are just there watching and taking in information.

But at the time you are proposing Justine was taken, she wasn't on the inside watching.  That's the whole point.  She's not worth taking before she was in a good position to do that.

Or because Justine was already possessed, Susan couldn't have fed on her if she wanted to.

Go read the end of GP.  Justine was fed on by the other rampires.  She shows Harry the bite marks.

That isn't Lara's style.

It would have been kind, and Lara is sometimes quietly human when nobody is looking.

Yes, but that was before Margaret's curse, Papa Raith isn't the man he used to be.  He wasn't going to use Nemesis to take out Thomas, but use Thomas by way of Justine..

Papa Raith never fed on his sons, only his daughters.  Nothing changed there post-death curse.

Justine can still do a great deal of harm.  Who knows what secrets she had access to as Lara's Privy Secretary.  Granted, some of that information will eventually go stale, but there will be more damage to the White Court for certain.

One easy example: Justine/Nemesis knows that Lord Raith is a drooling moron.  That is not public knowledge, but suspected by some. 

Another easy example:  Justine's "betrayal" of Lara demonstrates Lara's relative incompetence at scheming, justifying (more) plots to depose her.  Yes, many of her serious enemies died during Blood Rites and Turn Cloak, but many remain, certainly.

I'd imagine any secrets would very quickly go stale.  Moving safe houses and the like.  Swapping security protocols in the Raith estates.

After this long, I think Lara being the White Queen is an all but open secret (especially to the people that play the information game like the White Court).  She's pretty well solidified her power base beneath her in WN (finishing up in TC) and has been expanding White Court power politically through the mortal world (remember the navy cruiser in Changes?).  You don't move like that if there's a real threat of your base of power being ripped from under you.  Losing Justine is a hit to her, but I don't think it'll make other whampires think it is time to take a shot at her.  If anything, I think losing Justine would be an emotional toll instead of a political one.  Lara probably doesn't have that many close friends, tbh.

Um, black sheep, a little crazy?  Sounds a bit like Maeve doesn't it?  Hmmm... Target, the brother of a star born who defeated He Who Walks Behind at sixteen...  I'd say perfect positioning.

Maeve is several orders of magnitude more important than Justine, and if your goal is to get a handle on Harry originally from before BR, his brother's mortal girlfriend is not a good target.  Might as well get Harry's dentist. 

No, she wasn't random, I'd have to go back and read, I seem to remember she was selected kine to feed the family, I seem to remember Lord Raith chose her for him.

Thomas met Justine at Zero.  A citation would be nice here.

Why?  Yes, that is what she ended up as, but what she did, she didn't need to be secretary.  All she had to do was become the lover of Thomas, and then get herself pregnant, she then had all the leverage she needed to get him to upset the apple cart.

Without the rest of her connections, she blackmails Thomas, he gets disavowed and executed.  All that work over the course of years for no payoff.  It's not worth the effort for Nemesis without Justine's other connections.  Nemesis couldn't have predicted that Justine would get all those connections before BR, hence infection post-BR.

It may appear random, but not really, as a male, Raith saw his son as a threat.. The choice was a bit more complicated than merely random.

Papa Raith had taken care of several sons before Thomas and probably planned on taking care of several more in the coming centuries.  Nemesis doesn't need to be involved for that.

However that didn't happen, I think you are confusing the end of Grave Peril with Changes.. Susan only becomes a full feeding baby vampire in Changes and we know what happened there, Justine wasn't at C.I.

I'm not getting GP confused with Changes.  Check out the end of GP again. 
Bianca locks Justine in the larder with half-turned Susan.  Until Harry showed up, it was obvious that Justine was intended to finish her turning.  Huge chance that the effort of infecting Justine before BR is all wasted.

In Grave Peril Susan is half turned, but she didn't feed, now they may not have gotten to Justine yet, but Mavra was also there and chose some "take out" when she left, those poor kids were also unturned.  So perhaps Justine got lucky or she wasn't messed with because she was already possessed by Nemesis..Again, my point, how did she survive?  Oh maybe she is possessed by Nemesis..

Or maybe it was completely unpredictable luck that Harry managed to save her against all odds.  Other rampires had already started feeding on Justine before she got locked in with Susan.  Justine was set up to die that night from Susan's first feeding. 

Not so odd, Lara loves her brother and is grateful and knows how he feels about her. Either way it embeds Justine further and makes her even more legit, best cover yet.

You've got a 50/50 shot that Lara buys her a country house to stay in far away from WC politics.  That's a 50/50 shot that half the benefit of taking her is wiped away and Nemesis wasted years of work recruiting a nobody.

Nemesis has time, this isn't the only place that Nemesis is, it is a critical place, things don't always go exactly right, just look at how Harry's life has gone, it is full of "what ifs" and "but fors"  Nemesis isn't always successful but that doesn't stop it.

Exactly, the world is difficult to predict.  Nemesis plays the odds and spends its effort to acquire well-placed agents most likely to be able to help its agenda.  You don't invest your power in a nobody and hope for the best that you'll get lucky.  Justine wasn't worth acquiring until after BR.

Or infected before, there is motive you know?  If Lord Raith instigated it for example, then he pushes
Justine together with Thomas.  He both would like to get rid of Thomas and he knows who his brother is.  No, the more I think of it, the more likely she was always infested.

No, not evidence for infecting her before, because Justine wasn't anywhere near that strategic position that makes her worth acquiring before BR (really before WN imo).  Before BR, Justine was black sheep of the family Thomas's mortal girlfriend; that's basically it.  There were much better targets for Nemesis to spend its finite resources on before BR.

I don't see Thomas's character growth being based on a lie.  His growth came from his own feeling, that was sincere, not his fault if he was duped.  Justine wasn't trying to get pregnant out of love for Thomas.. That weren't a dream.

Like I said, your mileage may vary.  Taking Thomas's character arc to "Psych, she never really loved you" is not a good storyline for me.  I don't think that viewpoint would be uncommon.

Nemesis is a very good chess player, that is what makes it so dangerous.. So dangerous in fact that Titania only whispers it's name.  As I said, implanted Justine is no random mortal, just sat back quietly acting a bit crazy to take advantage where ever she could and she did.

Before BR, Justine really is just some random mortal that Thomas fell in love with.  Her choices and circumstances elevate her position only after BR, which makes that a good early bound for when Nemesis got its hooks into her.

For mortal Justine to be worth the resources for Nemesis to grab, she needs to be secretary to the White Queen at least.  To have predicted Justine from the beginning was going to get there requires Nemesis to correctly guess
1)  Random mortal Raith picked would be compatible with Thomas for more than a fling
2)  Justine would need to survive not being eaten by baby-rampire Susan; and that probably only happens because Harry intervenes in time.
3)  Justine survives fatal feeding from Thomas
4)  Lara takes Justine under her wing instead of setting her up somewhere quietly out of the way
If any one of those things doesn't go exactly right, Nemesis loses out on its investment of resources in the Justine plant.  Nemesis would have had to predict all of those unpredictable outcomes years in advance.  If it could do that, Nemesis should have ended reality centuries ago.

Ummm...What? Are there some short stories floating around post BG that haven't been shared with the public?

There are some microfictions posted on Jim's website. Microfictions here
They're short and character driven.