It is a long, hard, painstaking process. She has to come at it from both ends - peer at possible combinations of her symbols to see what makes sense, and come up with a visualization of her desired end result so she knows what parts she needs to build. She's never done this before, and keeps having to go back and edit things. One of the fourth-tier parts has so many third-tier parts in it that she takes weeks of trying just to hold them all in her mind at the same time and make them snap together into a single object she can keep memorized in its entirety. She spends a stack of notebooks as high as her waist working out another fourth-tier part, only to discover that she's got a key "word" wrong and has to start completely over because it affects everything else.
When she starts, she resigns herself to the possibility that her spell will take an entire year.
This estimate is soon revised.
It takes half a century of stolen time and backtracking and double-checking.
But it will be worth it, she thinks, if her mother will love her unreservedly, if she can keep up with Thor, if she can put her scepter - now a bit short for use as a cane, for a child her size - aside and run and dance. (If she can do magic.)
And once she casts it, it will stay forever.
She has just about built herself from atoms; there are separate bits of this spell for each muscle in her body in its current shape and accounting for its future growth (she's been reading anatomy) and connecting them all to her mind, directly, commanding their obedience.
She assembles the ninth-tier pieces into a single, unified whole, and it shines bright in her mind, and she knows exactly what to do with it, from cube-inspired knowledge stamped as bright in her thoughts as though she'd touched it yesterday.
It's all together now.
She wills it.
She knows the difference at once though there's no visible effect - even in how she holds up her head, how the last page of her notebook feels under her fingers.
She wants to get up, twirl, leap, pick up her scepter and brandish it like a sword, run down the halls whooping and show Thor.
But she doesn't. It wouldn't do to be conspicuous. (Heimdall is watching; she can't read the cipher but she can see the results.)
Loki is going to have to pretend to have outgrown her clumsiness, spend the next ten or fifteen years still tripping occasionally but less and less. Maybe she should get new shoes; maybe she should ask about learning to dance. Some outward excuse. Something less sudden.
She sketches a plan in her non-magical cipher, and sets about enacting it.
(Meanwhile, she contemplates what spell she should build next.)
She has also never stopped suggesting that Loki take up this or that physical activity, holding out the hope that maybe this is the one she'll be good at. She remains undiscouraged when Loki declines to try them.
Dance is the next thing she suggests.
(Meanwhile, Loki has decided to work on healing spells. This will have to be several different spells; there is just no compressing it into a single, perfect work of sorcery. It will certainly take hundreds of years, especially now that her time is divided yet again with the pursuit of various appropriately womanly things. But it could come in useful.)
And Thor has set her sights on the hammer - not hammers in general, but a particular hammer, one that currently rests on a pedestal in one of Odin's finest treasure rooms. It is reasonably common for a warrior to ask permission to lift it, but in the last several hundred years, no one who has tried has ever succeeded.
Many of her healing spells will share similar foundations, so she makes a lot of progress in the first fifty years of work on the suite, and she also has to re-do fewer pieces now that she has the graceful spell under her belt. She has one that should work on serious injuries by her five hundredth birthday; it's the simplest, and she expects at least another century to go by before she can cure disease. She might put the spell intended to address non-injury-based deterioration aside for a while, once its pieces no longer overlap with the others.
The only really old person she knows is Odin, who she would never dare heal and might not want to anyway.
When Thor has grown to almost her mother's height, still a child but now close to becoming an adult, one day she challenges that lady to a fight again. And wins.
Loki can run quite lightly and quite fast, even armored.
In the event, they do find tracks; finding this bear has never been a problem. Thor suggests that they dismount and lead the horses along the trail; she has never used Mjolnir before and is sure she could not wield it from the back of a terrified horse.
It is much, much larger than anything or anyone Thor has fought before. Its shaggy hide is dotted with the broken ends of old arrows, and scars from the swords or axes of previous opponents. Its paws are each individually bigger than her head. It could bite her in half with a single chomp and not take much trouble about it.
She takes a deep breath, raises Mjolnir, and charges with a yell as thunderclouds fill the sky.
...Loki's spell cannot actually resurrect the dead. And she would need to be conscious to cast it, even if all the difficult work of assembly is over and done. She suddenly regrets this very much, wishes she'd run and told Father, but there's nothing for it now. She circles around, looks for advantageous terrain - they'll need all the help they can get. At least she and Thor can flank it.
She does not expect the bear's head to snap back with a loud crunch, nor for the hammer to keep going, dragging her arm in a full circle until she wrests control from it at the last moment and hauls it up to strike at an incoming paw. Claws screech on metal. Thor lets the hammer's incredible momentum spin her in another circle, and when she comes back around she dips low and swings high and leaps for the bear's face.
Well, Loki's a little redundant, although she may have usefully distracted it. That's all right, Thor is okay so far, so is she, that's the point. She drops onto her stomach at the edge of the ledge she's standing on for reach and stability, stabs down at the bear's stomach; she'll be on her feet in a moment if it gets its footing back.
Thor stops hitting it when it stops moving; she jumps off, rolls, comes up facing the bear's corpse, and backs away warily, because with beasts like these you never know.
It remains dead.
She laughs.
"Sorry I didn't leave any for you, sister!"
Loki likes the taste of mead just fine, but not what it does to her brain in any quantity. She accepts it, drinks slowly, and makes much of the also-delicious spiced fruit juice that is made available, of which she consumes a much greater quantity. She should have the healing spell for poison handled soon and then she'll be able to drink anyone she likes under the table, sing the runes backwards, and wake up the next morning chipper and free of discomfort; that will be nice.
They are not in trouble. Thor is treated with all the respect of an adult warrior, tempered with a certain amount of hair-ruffling, and Loki gets to sit in the halo of her sister's sudden fame and drink exactly as much mead as she feels like, because no one is counting tankards at this feast.