So one trouble with groups like this is always that we don't know much about the ponies in question. In this case, we don't seem to know much about her, except that she's super strong and trying to hide it. She also looks pretty happy to be helping out by balancing that merry go round on her head and helping out.

It kinda makes me wonder if she's hiding her strength because she's secretly a superhero or something! I think she deserves an origin story. And I'm still wondering about that cutie mark.

Anypony else have any ideas about her, or is anypony working on a story with her?

--Sweetie Belle

She's the result of over a thousand years of carefully matched arranged marriages, with every foal examined carefully and then paired with other likely candidates for the desired result. At last, the mysterious organization guiding the process has achieved their goal: a pony of truly super-equine strength.

She's the Kwisatz Haderach of earth ponies.

4781200

You sure that isn't Lazarus Longsocks?

--Sweetie Belle

4781193

How bout, like, she was bit by a radioactive hedgehog or something?

4781210

Her special talent is being bitten by radioactive hedgehogs? I didn't really think you could be good at that...

--Sweetie Belle

4781218

Well if you get superpowers out of it then I'd say you're pretty good at it! And it's more like, the hedgehog represents her radiation-granted super powers. A superhero pony would need a cutie mark that wouldn't immediately show to everyone they're a superhero, no? That way they can have their secret identity.

4781220

I suppose that could work, though she'd need to figure out something to tell everypony that her cutie mark was for. And then you have to wonder how Diamond figured it out, since she clearly already knew 'bout it. Unless Lily's just really bad at hiding it, and keeps accidentally using it where anypony can see...

--Sweetie Belle

4781226
Oh, right -- I forgot to address her cutie mark.

Obviously, she received it after using her incredible super-strength to subdue Spiny Norman.

4781193

The cutie mark is most likely a reference to something the show has referenced before: The Hedgehog's Dilemma.

It's meant as a metaphor for the challenges of human intimacy and was first described by one Arthur Schopenhauer in a one of his books. The exact description he uses is...

A number of porcupines huddled together for warmth on a cold day in winter; but, as they began to prick one another with their quills, they were obliged to disperse. However the cold drove them together again, when just the same thing happened. At last, after many turns of huddling and dispersing, they discovered that they would be best off by remaining at a little distance from one another. In the same way the need of society drives the human porcupines together, only to be mutually repelled by the many prickly and disagreeable qualities of their nature. The moderate distance which they at last discover to be the only tolerable condition of intercourse, is the code of politeness and fine manners; and those who transgress it are roughly told—in the English phrase—to keep their distance. By this arrangement the mutual need of warmth is only very moderately satisfied; but then people do not get pricked. A man who has some heat in himself prefers to remain outside, where he will neither prick other people nor get pricked himself.

And, before you think I'm smart, this all comes from Wikipedia.

Anyway, in context, this could be a reference to how she is insanely strong, but fears her strength to a certain extent. It's not exactly hard to imagine a filly like her having more than a few instances of not knowing her own strength and accidentally breaking something or hurting someone. Which would explain why she doesn't like the idea of Diamond Tiara letting everypony know about it.

However, as with DT's own cutie mark, a positive spin may be put on hers. A hedgehog's spines at meant as a natural defense, meaning that our super strong filly here may have a talent for defending others form harm. She might grow up to be either a royal guard or (as some have already jokingly pointed out) a real pony superhero.

4781193
The question that I think is in far more dire need of answering is; where exactly are these long socks I was promised?
We've desperately needed ponies in socks for ages! And they blew their big chance.

4792986

The hedgehog represents how prickly people get when they realize she doesn't wear socks.

4781193

It kinda makes me wonder if she's hiding her strength because she's secretly a superhero or something!

EXACTLY my thought! Was thinking that right away after having watched the episode a few times and once my mind slowly opened itself to other impressions from the episode aside from the BIG EVENT of Applebloom, Scootaloo and Sweetie Belle getting their cutie marks.

After recognizing her enormous strength, I distinctly remembered that I have once read that hedgehogs have a, for their size very surprising, strength and can lift things much bigger and heavier than them. I was just researching about hedgehogs, but I couldn't find anything about that, so I was completely confusing the hedgehog with another animal.
But I found something else interesting while researching:

Hedgehogs bend their legs while walking most of the time, so that their bellies touch the ground in order to not having to carry their own weight the whole time. In other words, hedgehogs are actually very weak, not even able to carry their own weight for a longer period of time.
So her cutie mark does definitely not stand for her amazing strength.
SaintAbsol's theory is spot on. It fits so well, I can't think of anything else what her special talent could be and what the hedgehog stands for.
Little filly is definitely a superhero who is only active at night (because hedgehogs are too).

4781193 This might be a stretch, but is there a possibility Lily might be Cherry Berry's daughter?
Am mostly basing this on coat colour. The mane style and cutie mark type vary (why I went along with daughter instead of sister).

Since Cherry flies a lot with the Twinkling Baloon, it is potentially bossiness that caused Lily to acquire super strength. (If the sun is considered magic, then it can nea dumped it radiates magic, and Lily got a stronger dose of it, since she was exposed more to it prior to birth.)

4852944

You should collect more clues for that and then open an own thread for it. This one is for pictures only.