Squirrel Girl/WMG

Squirrel Girl doesn't have squirrel powers.
Those are trained squirrels. She's Veruca Salt. After being thrown down the garbage chute she became obsessed with getting an army of squirrels. Daddy got her one squirrel, but she traveled the world, getting more squirrels to join her and she trained them to attack whoever she doesn't like. She went through Character Development and chose to be a superhero later.

Squirrel Girl doesn't have squirrel powers.
Squirrels have Squirrel Girl Powers.

Squirrel Girl is the daughter of the Beyonder.
Her powers have not fully manifested themselves, but she unconsciously warps reality around herself. This allows the fourteen year old girl to beat heavy hitters of the Marvel universe who should otherwise mop the floor with her.
 * Word of God is that her Squirrel powers are her only powers. How much of that you believe is up to you. Maybe she's the Marvel Universe counterpart of Teela Brown, and was just Born Lucky.

Squirrel Girl's real power is Plot Armour.
This is a minor power for almost all super heroes but she has made it her primary tool. That squirrel stuff is stage dressing, she would still win of she spent the entire time naked, bound and gagged and at the bottom of a volcano.
 * Sounds hot. Wait how old is she again?
 * Sounds hot? Oh my god.
 * 16-18. It's a little unclear at times.
 * Deadpool notes she's underage and therefore illegal so she's most likely 17.
 * Ages down to 16 are legal in some parts of the United States.
 * This troper would so read that comic.
 * It is worth noting that Deadpool noted that she was underage something like two years ago.
 * Then again, this is like saying "Bruce Wayne's got to be pushing 70 by now.."
 * Does that matter with Batman?

Squirrel Girl is a student of Miaowara Tomokato, the Samurai Cat.
Tomokato was the original practitioner of the martial art based on the Dark Side of Absurdity, which allows the wielder to exercise effective omnipotence and beat any foe, however cosmic, but only if the audience is laughing. Does this sound familiar to anyone? Add in that Tomokato is himself a time-traveling and parallel-timeline-travelling anthropomorphic furry animal, and that his first candidate as his protege (his nephew Shiro) is a hideously unlikeable psychopathic brat, and its not unlikely that at sometime throughout his wanderings through all time and space, he met the utterly charming Doreen and decided that she was a more worthy successor to his school. (The character of Miaowara Tomokato is from the Samurai Cat novels by Mark E. Rogers).
 * Supporting this is that its canonical that among the very long list of fictional realities Samurai Cat has visited is Hyperborea, which as we all know is part of the ancient past of the Marvel Universe. So he is entirely capable of having traveled to Earth-616.

Abilities pertaining to Squirrels are the ultimate power.
Power over Squirrels is no laughing matter, Doctor Doom, Maelstrom, MODOK, Terrax, and Thanos never really had a fighting chance. An army of Squirrels is far more formidable than any force of Doombots, Hydra, Skrull, or Mutants. Thank god Squirrel Girl is on our side or we would all be kneeling before our tiny furry Squirrel overlords.
 * Don't say army of squirrels. They are the one set of our new overlords I, for one, would not welcome. Rats in fur coats.
 * Don't let Grace hear you say that.

Squirrel Girl is the daughter of The Janitor
Undefeatable squirrel army? Mighty fearitude? Please. It's obvious.
 * That... That actually makes sense. She's got such an affinity for squirrels because she's training to lead an uprising against her father, for the safety of squirrels everywhere (let's hope she never hears about him trading his squirrel army for a stuffed dog).
 * Doesn't quite work--her name's Green, not
 * And you believed that?
 * The first thing she and her mom did after moving to hide from The Janitor after he discovered them plotting rebellion was change their names.
 * Alternately, she's the daughter of the other Janitor

Squirrel Girl's using an infinite loop.
Obviously, she has Earthcraft, Squirrel's Nest, and a Forest in play.
 * That's actually disturbingly plausible

Squirrel Girl's secret is she's a DC character trapped in the Marvel Universe
She's able to do everything she does witha happy-go-lucky outlook on life, is confident, well-adjusted and straightforward, and manages to do it all with no Angst. The excessive Angst typical of Marvel characters, such as Speedball becoming Penance, drives her crazy. If she was in the DC Universe, she'd be utterly unremarkable and typical.
 * Actually, this explains why she can't die either. When Marvel and DC do a crossover, they aren't allowed to kill each others characters. So, no matter how deep a hole Marvel puts Squirrel Girl in, she's gonna get out because she's a just a DC guest character.
 * She would fit in well with the Legion of Super-Heroes...
 * Eh, the DC Universe isn't much brighter than the Marvel Universe these days (just ask the Batman family). It's obvious that Squirrel Girl is from the only active comics title with a Golden/Silver Age sensibility -- Astro City. She fits in perfectly with characters like Jack-In-The-Box and the Furst Family, and wouldn't be out of place if she joined Honor Guard...
 * That's why Batman sent her to the Marvel Universe. 1: If they fought the universe would implode. 2: He doesn't want the competition. 3: He doesn't want the smiles. She could go home but LIKES Marvel better for some reason.
 * Cause Spidey's a barrel of laughs?
 * She's from the Pre-Crisis DC universe.

Squirrel Girl is Doom's next target.
The closest thing Doom has to a gimmick is stealing the powers of superbeings (Silver Surfer, Galactus, Beyonder, Haruhi Suzumiya). Doom seeks to steal the power of the being that defeated him with mere squirrels. Surely such power would be the best weapon in his neverending battle against RICHARDS!
 * Doom can't steal Haruhi's powers, silly boy. Because Squirrel Girl is Haruhi! (I know, it's cliched; but what else do you want me to say, that she runs on Spiral Power?)
 * Don't be ridiculous. Squirrel Girl doesn't run on Spiral Power. Spiral Power runs on Squirrel Girl.
 * Ouch. Does it leave footprints?
 * No, everyone knows there is no Spiral Power in the Marvel Universe. It's too afraid of Squirrel Girl.
 * In Squirrelian Marvel U., Meta Origin originates from you

Forcing Squirrel Girl to learn the word "impossible" will rob her of her powers.
She accidentally blabs about it during a battle with MODOK. What do you mean, I'm being too literal?
 * It all makes sense.
 * So her real power is Clap Your Hands If You Believe, she just believes she has squirrel powers, and is too awesome to lose

The Thanos Squirrel Girl defeated was neither a clone, nor the real thing.
He was a Skrull. Possibly anal.
 * The Watcher confirmed without a doubt that the Thanos she defeated was the true Thanos.
 * Except Thanos said he could create clones that could fool even the Wactcher. Also, he's Thanos.
 * Meh, what does he know?
 * Where you live.

From Mighty God King: Squirrel Girl is Ratatoskr
In essence, Marvel is all about the Norse Mythology. Ratatoskr, a squirrel, is a relatively minor figure who relays messages between the top and bottom of Yggdrasil. The comment in question isn't too specific, but I think we're supposed to make something of the fact that, despite the 'messages' being primarily insults, Ratatoskr came out of it all okay, without any maiming, or the like.

Squirrel Girl will be directly responsible for undoing One More Day (and much more).
In the first page of the Crisis Crossover, Deadpool will provide Squirrel Girl with information about One More Day, and Squirrel Girl's fangirlish attitude towards real superheroes like Spider-Man will make her furryious, thus she embarks on her quest to defeat Mephisto, whom she defeats in the most epic and breathtaking fight ever shown. The ramifications of this event will affect the Status Quo of the entire Marvel Universe. Firstly, it will reveal that Peter Parker never sold his soul to the devil, he just divorced Mary Jane and accepted his child with her like any normal, sane, goodhearted person would do. Secondly, it will show that all of Reginald Hudlin's work of Black Panther will be revealed as a patriotic Wakandian's own deal with Mephisto in a foolish attempt to make Wakanda greater than it was. Thirdly, it will reveal that Norman Osborne and Aunt May, who were both revived during the Clone Saga, are really was clones all along, made by none other than Mephisto.
 * It will be revealed that the woman that everyone thinks Peter Parker should be dating is in fact an Eldritch Abomination that is the REAL (in universe) cause of all of Quesada's changes, and Squirrel Girl will singlehandedly destroy it, thus undoing everything that had happened.

Squirrel Girl has some relation to the Lady of Pain
The Lady of Pain and Squirrel Girl are both, mysteriously, more powerful than just about anything else in their respective multiverses. And one source theorizes the Lady of Pain is six squirrels and a ring of levitation. Obviously this means they're cross-dimensional equivalents or possibly Squirrel Girl is the Lady's daughter.
 * Given that Squirrel Girl can command squirrels, and we are here assuming that the Lady of Pain is, in fact, squirrels, it is more likely that Squirrel Girl is The Man Behind the Man to the Lady Of Pain. Obfuscating silliness?

Squirrel Girl really is half squirrel.
Her mother made up the "mutant" story to hide the shame of the Interspecies Romance she doesn't like to talk about.
 * Actually, it could be him:

Squirrel Girl really is a super powerful meta-human...
It's just that she's gotten so sick of the world that had become such a bleak, dark angsty place that she's decided that if she had to save the world, she might as well be a Bunny Ears Lawyer and have some fun with it.
 * So sort of an Anti-Superboy Prime...?

Squirrel Girl isn't a girl with squirrel-like mutations, she's a squirrel with human-like mutations.
Her mother is adoptive.

Squirrel Girl will be reinvented as a Darker and Edgier Anti-Hero when a sufficiently bad enough writer gets their grimy hands on her.
I'm sorry. But given Marvel's track record in recent years, it's inevitable. Soon, SG teams up with The Punisher. They Fight Crime.
 * It will be still hilarious, but in a different way...
 * It'd be better if she teamed up with the Punisher, but without any changes to her characterisation.
 * Sure would. Too bad about that.

Squirrel Girl's father is Chuck Norris.
Because Rule of Cool.
 * Of course! And her mother is another Memetic Badass!
 * Her mother is Unohana.

Squirrel Girl's actual power is Reality Warping to follow the Rule of Funny
So long as she keeps the situation completely ridiculous, she can make anyone her bitch. Since commanding squirrels always makes the fight weird, she can beat Doctor Doom and the like.

Squirrel Girl's power comes from having Spiral Power
Because no one else in the Marvel Universe has access to Spiral Energy, she's the most powerful being in it. She also expresses her Spiral Power in a slightly different way, just by being upbeat, cheerful, and genuinely happy, rather than hot-blooded. In other words? She's Nia, but with squirrels.

Thanos was lying.
If his duplicates can supposedly fool even the Watcher, he can remain tecnically undefeated from the point of view of anyone in-universe. Mostly, he just didn't want to admit that he got his butt kicked by a girl with a fluffy tail.

Squirrel Girl's so powerful because the Marvel Universe runs on the Dwarf Fortress engine.
Someone made the squirrels too hardcore.

There are super-squirrels.
She controls these squirrels, and they have the best powers: invincibility, invisibility, creating alcohol, giving people a temporary Weaksauce Weakness...