Aslan didn't bring back Peter- Lucy did.
Lucy's first time through Narnia, she trusts Aslan, even if she doesn't always believe in his decisions. She believes that he makes more good decisions than bad, that he is a benevolent guardian of Narnia.
That doesn't stop her from being curious, however. She ventures out into the wilderness, not stopping to gather her guard to her, and finds Old Magic. She learns her own magic from an old witch living in the oldest cave in Narnia. She learns Magics that heal, that come close to the power wielded by the cordial. She seeks to help as much as she can, to do good by the world she loves.
But that was before she was ripped from her kingdom. That was when she was complacent, believed that Aslan was all-good.
(She is not innocent- none of her siblings are. Ruling a kingdom for fifteen or more years changes a person, exposes them to some of the true horrors of the world. Then, losing thay kingdom, having it ripped from between your too-mortal fingers- that scars you. Drains you.)
Now, in Caspian’s age, she has so much free time, no one watching her every move, and every reason to want to find new worlds. She pores through the oldest of journals, seeking answers to questions that never even occurred to her in the Golden Age.
She finds that cave again. Her witch is gone, but the witch's apprentice's apprentice's apprentice is there. The new witch recognizes Lucy as the queen of witching legend, the one who treated all witches with respect. (The queen who asked questions that no other Narnia dared.)
"Come in, Your Majesty," the witch says, and Lucy smiles.
"No need for titles, jakintsua," Lucy says.
Lucy has a different motive now, in this second round of learning. She has been ripped away from her kingdom twice now- she wants to learn everything she can about what happened.
(She has always been curious; now, though, that curiosity is focused. It is calculated. She wants to know about the worlds beyond this one, the worlds that Aslan could have ripped her and her siblings away to. She wants to know what world Aslan himself came from and how to get there.)
Lucy learns of the power contained within the Lamppost, of the way this world came into being. She learns the ways that magic flows through Narnia, the ways that it connects every life form and rock.
She learns how to separate the walls between worlds, how to pass from one world to another.
The witches tell her magic relies on great emotion, on significant moments and revelations. They tell her betrayal works well to power spells, as does commitment- every action has an equal and opposite reaction, they say, and the same goes for magic as for gravity.
She doesn't use the great glade of legend, with the trees that the legendary Diggory and Polly used to cross from England to Narnia. She uses the wardrobe- or, at least, its exit in Narnia. The very tapestry of the world around it is woven with Deep Magic that can be used to power all manner of world travel, if one only has the talent for it.
And oh, does Lucy have the talent for it. The witch cannot be sure where it comes from, whether it is Lucy's previous travel between worlds that primed her body and magic, but they are both certain of the breadth of Lucy's power. Its evidence is quite clear, after all.
(The only catch is that she can't transfer herself to England- she can only pull people in her direction from that portal. She never learns why this one world is barred to her, why the greatest of Magics doesn't work on this singular portal. She eventually makes her peace with it, though. Every world in existence is open to her save the one- that is such a small sacrifice to make.)
She never tries to pull Susan though the wardrobe. She knows her sister, knows that being pulled back to Narnia would make her deeply unhappy.
(Pulling Luna, Millicent, and Blaise, some of Susan's sons’ friends, is something Lucy does do, some years down the line. She knows that these three have much to learn from Narnia, and Narnia has so much to learn from them.)
She pulls Peter into their world this way, gradually pulling on the threads of his and Anna-Mae’s life magic. She is inexperienced in this trip, one of her first, and thus it is slow and she's actually surprised by when they finally arrive in Narnia. She had actually gotten distracted by Eustace and their adventures, by the land she used to roam freely through. This world had always drawn her, with its freedom and her family so close to touch.
Once her oldest brother is here, though...
Edmund and Caspian have an excellent grip on the affairs of Narnia, and they don't really need her help. There are a thousand worlds that do, though.
She begins to travel worlds, begins to meet people from many different universes and falls in love countless times.
She kisses Tiger Lily in Neverland, dances with the Indian Chief around fires and down black-stoned beaches. She fights pirates, flies with Lost Boys, uses her cordial on a dying fairy.
She uses her cordial on victims of disasters plaguing a world named Panem, spends two heartwrenching weeks falling in love with a girl named after a flower before watching that girl get blown to bits by a bomb built by her brother.
She travels to a world named after Wonder, seeking to lose her mind for awhile. (And she does, playing hundreds of games of chess in a row before an unfortunate encounter with the Queen of Hearts that ends in a Hatter losing his head).
Lucy is named Valiant for a reason. She is armed with medicine and dagger, with defense and offense. She is no shrinking violet, no soft-skinned maiden- she turns her desire to heal into a weapon unto itself.
She wades into battlefields in the Underland, in Middle-Earth, in the Demon Prison, in the Land of Opium and in a hundred other worlds. She helps save thousands of lives, whether soldiers or victims or children.
She enters Dying Worlds where she stumbles through the last dregs of civilizations. She witnesses the ends of empires thousands of galaxies across, watches infant worlds take their first breaths in the wreckage.
(Once, she opens the Wardrobe doors into a world that threatens to blind her with how incredibly bright and endlessly dark it is at the same time. This is one of the Final Worlds, the one they call Aslan’s World. It is blocked to her in her first travels, before she truly grows into the full extent of her powers.
Eventually, though, every world opens to her fingers. She makes it to Aslan’s World, his Final World, and she finds every friend of the Pevensies from the Golden Age. She finds Ravenna and Samar, a woman Lucy once courted. She finds Kavé and Greeley, finds everyone who died in battle and famine and of old age.
And she realizes that this world is not perfect. It is not the paradise that everuone believes that it is. Lucy knows she could do far better in the creation of her own world.)
(There are worlds in which she is worshipped, in which her very name connotes power.
In Narnia, Edmund's name in made immortal. In England, Susan leaves her stamp as the adoptive mother of the Chosen One. Peter and Anna-Mae come to be known as the founders of a Golden Age of medicine; Caspian is one of the two Warrior Kings and Eustace, the Once-Dragon, is one of the greatest knights Narnia has ever known.
In a thousand worlds, Lucy is called God.)
Lucy has not been innocent since she was a child. She carries the Deep Magic in her veins, holds the powers of life and death in her hands. She can break the universe apart, shatter entire armies with a single whispered word.
She has become a goddess, and she understands Aslan so much more intimately than anyone else. She knows he cannot possibly be all-benevolent, cannot be selfless and righteous in all the ways she used to believe he was.
She is not, after all. No God is. Each operates according to their own wishes, their own agenda.
She knows that if her family was threatened, if Narnia was threatened- well, she carries the power of the Deep Places. Her fingertips can tear the fabric of reality as easily as one rips a page of paper.
Let Aslan do as he wishes, as long as he does not cross her. If he does, though...There is always a hierarchy, and among gods it is based on power. Lucy knows the Deep Places. She knows Old Magic, stretching back to worlds such as Avalon and Yomi and Shambhala and all the other places that were ancient when Aslan learned his first Deep Word. She knows what made Aslan, and she knows how to unmake the magic holding him together.
The White Witch's mistake was using the Deep Magic that Aslan himself breathed into being- Lucy's power comes from a far older, far hungrier place.
(In another world, Lucy's sister will think her a Gryffindor, bravery and chivalry at her core.
Susan will be mistaken.
Lucy is Ravenclaw. She is curious, hunting down knowledge without regard for consequence. She carries honor within her heart. She is ready to shatter entire worlds to right wrongs, to make things just.
Lucy is valiant, but she is also a healer. She mends things when they are broken. She helps people get back on their feet, to heal after great trauma and sorrow.
She also knows well enough to eradicate things that are rotten.)
Curiosity killed the cat, as they say.
Lucy Pevensie smiles grimly. They couldn't be more correct.