Forgive me if this is kind of obvious, but...

Harry made a deal with Lea for power prior to the series beginning.

In Summer Knight, Lea traded the debt to Mab. Mab and Harry negotiated the debt could be settled by Harry performing three services. Mab states that the first favor is to find the killer of the Summer Knight.

At the end of Summer Knight, Mab offered to cancel the debt in exchange for Harry taking up the Winter Knight mantle. Harry refused, two more favors were still owed.

In Small Favor, Mab tried to collect on the second favor. Harry balked. Mab again offered to cancel the debt in exchange for Harry taking up the Winter Knight mantle. Harry performed the favor, finding Marcone. At this point, Harry still owed Mab one favors.

In Changes, Harry approaches Mab with a deal to accept the Winter Knight mantle in exchange for her healing his broken back, give him power to rescue his daughter, and that she not force him to kill anyone he loved. Harry fails to mention anything about the third and final favor.

Mab can't order the Winter Knight to kill, say, Molly. (Like she's ordered the Winter Knight to kill Maeve) But she could require Harry Dresden to kill the Winter Lady in order to fulfill the third favor.

Sword of Damocles, indeed.

Let's agree that Uriel is immortal as long as he retains his grace.

Harry's already been halfway to the other side, a soul is immortal.

Being unaging and naturally deathless is not the same as immortal. Mab is not immortal. She was not born immortal. She became immortal when she took up a fae mantle.

I'll refer you back to Bob's words in Cold Days. After about a decade, the person is lost behind the mantle. We've seen glimmers of this with Molly. Maeve entered Harry's birthday party bucky bare-assed. Molly did her "Welcome to the Jungle" entrance in Battle Ground clad only in frost. I'll be interested to see if Molly starts taking on Maeve's crazy, cock-tease personality.

Mab has been the Winter Queen for almost a thousand years. The mortal Mab can only peek out from behind the mantle on the Summer Solstice, when Winter has its weakest hold on her. She is mostly mantle at this point. Very little of Mab remains, on a day-to-day basis. But there has to be something left. Perhaps that's why the prior Summer Mother resigned?

In any event, Butcher's going to tell this tale sooner or later.

After the wedding Harry will no longer have protection from Lara. The wedding vows are a spell that removes true love protection. See Something Borrowed for confirmation.

Choice plays such a big part in mortal affairs, that stripping someone of their free will by saddling them with a mantle seems sure to draw down the response of The White God.

Especially if we find out at the end that it was Hecate evading TWG's edict to give up their immortality or withdraw from the mortal world. My theory is that she did both, and didn't. We'll find out when Mother Winter (Hecate?) spills the beans.

Free will does not mean that everything that happens to you is somehow your choice. Being born was not your choice.other people make choices too.

Sure with some verbal gymnastics you can say that Molly chose to go to the island or you can point to several other choices she made in the past that lead to it but often what happens to you is not your choice, only how you handle it. Molly decided to take the job seriously

This is the "Sins of the Father" argument. The children bear the weight of everything their parents do. There's no way to make a fresh start and vendettas never end.

I’m not sure I’ve gotten all of this sorted out in my head, so I’m going to lay it out here. Feel free to jump on and correct any inaccuracies.
Back in pre-history, The White God told all of the other gods to vamoose. Give up your immortality and live on, or keep it and have nothing more to do with mortals.

Someone, probably Hecate, maybe the Norns, instead of giving up their mortality, sponsored the fae. The fae, who had historically been the foot soldiers defending the Outer Gates, the keepers of the Outer Gates got a promotion. Their sponsor split their immortality into at least 8 mantles, 6 immortal, two not. Set up the two fae courts, one, Winter, to lead the defense of the Outer Gates, and one, Summer, to defend reality against the Winter court.

But, and this is important, The two tripartite divisions that are the fae queens, are still immortal. And The White God’s edict still holds true, their power was ordered to stop messing with humanity, so they cannot truck with mortals. In Summer Knight it’s described as fae queens cannot directly interfere with or kill anyone who isn’t attached to the courts through birthright or bargain. They they can do so indirectly with trickery, guile or glamor. Mortals, however, can still deal with them, since free will trumps everything. Free will allows mortals to deal with Outsiders, it certainly allows them to deal with fae.

It’s my theory, although not confirmed, that the fae queens must always be mortal when endowed with a mantle. Titania and Mab are sisters. Mab revealed to Harry that she was mortal once. Logically, that means so was Titania. At best they were changelings, but unless they’d chosen fae before they were endowed with their mantles, they would still be considered mortal. Aurora, Maeve and Sarissa were their daughters, arguably making them changelings, but if my theory that follows is correct, that’s not so cut and dried. Lily was a changeling, but she hadn’t selected her fae heritage yet when Aurora endowed her with the Summer Knight mantle and turned her into a statue. When Aurora died, She was endowed with the Summer Lady mantle, while still a mortal, albeit one wearing a mantle. Molly, of course, was fully mortal when she was endowed with the Winter Lady mantle.

The mantles that are not immortal, went to the knights, the hatchet men for the fae courts. These are mortals who the fae can sick on other mortals, to kill or hurt. Because the fae queens are constrained by The White God’s edict. Sure, the knights also will bring the pain to the fae, but what sets them apart from the other fae mantle wearers is their ability to kill mortals.

Run of the mill fae can interact with, kidnap, kill mortals. We saw that all the way back in Restoration of Faith with the troll. Jenny Greenteeth would have killed Billy and allowed Georgia to sleep on. Phobophages, Malks, Rawbones, Trolls, you name it, they have all threatened or outright killed mortals all the way through the books.

But the fae queens can’t.

In Summer Knight, Slate, in cahoots with Aurora, kills Ronald Rheul, the Summer Knight. No problem there, knights are supposed to kill mortals. Aurora buys it at the hands of Harry’s minions. Essentially her death is at Harry’s hands. He might have been doing the slicing and dicing with the bane, but with fae logic, he was responsible. The run of the mill fae that wielded the box cutters, again, had no issue killing her.
Loyd Slate’s betrayal of Mab is also revealed in Summer Knight. But, instead of killing him and allowing the Knight’s mantle to flow back to her, she takes him prisoner and tortures him for years.

In Changes, Mab doesn’t kill Loyd Slate, Harry does.

Fast forward to Cold Days. Harry believes that Mab is trying to kill him over 77 days. But most of those attempts are through predators, traps or fae. She only tries once with a pillow and once with a shotgun. Harry, pre-Winter Knight, could have protected himself from a shotgun.
Mab orders Harry to kill Maeve because Mab believes Maeve is Nfected. Mab had previously cured Leanansidhe of Nfection. So, why didn’t Mab just do the same thing to Maeve, her own daughter in order to spare her life?

Because, even if Maeve was wearing a fae queen mantle, she’s still mortal. The mantle makes her into a high sidhe. The mantle is what doesn’t allow her to lie, normally. The mantle gives her the vulnerability to the bane. Just as the mantle endows her with immortality. And Kringle tells us later that mantles can be worn, exchanged or discarded. Which would imply that in order to exchange or discard a mantle, you have to possess free will.

The Nfection counters the mantle and allows Maeve to lie. It also allows her to kill Lily. Maeve is, in turn, killed by Karin.
In Peace Talks and Battle Ground, the Fomor servitors don’t get the mortal protection because they are involved with the Fomor, who are involved with the fae courts. Molly, Maeve, Sarissa and Titania are allowed to kill them with impunity.

In The Good People, Mab encourages Molly to let her mortality die. Molly responds by getting in Mab's face. Instead of bouncing her head off a solid object as Mab has done with Harry in the past, she accedes to Molly's wishes and lets her be.

I can’t think of any time in any of the books or short stories where a fae queen has killed or injured a mortal that is not involved in some way with the fae courts, either directly or through the Unseelie Accords. I think there's a strong possibility that the fae queens, with the possible exception of the only original queen, Mother Winter, may all have been, and still are, mortal.

Comments? Corrections? Amplifications? Thoughts?

Hell, Mab wouldn't do it because Mab would have to balance the scales.

She's a faerie. Killing Charity would incur a massive debt to the entire Carpenter family.

For one thing, she'd probably be on the hook for raising the rest of the Jawas, which would either result in a Evil Stepmother scenario or a hilarious sitcom plot about a faerie queen adapting to life in the 'burbs- possibly both.

I would watch the Hell out of that sitcom. And I don't like sitcoms.