Well… her dad has been revealed in one of the episodes.

@Background Pony #C099  
you have to interpret the text based on what preceded it, not what followed  
Maybe if you’re arguing a legal brief, but in terms of storytelling– or even IRL– that would essentially make a coherent narrative impossible; there’s a difference between what is presented to the audience on television and what is happening within the world being depicted. Twilight Sparkle as a character may not have had a brother before the Cold Open of A Canterlot Wedding, but Twilight Sparkle as a person living in a fictional world most certainly did; Shining Armor didn’t just instantly spring into being in-universe because he had never been referenced before. It doesn’t make any more logical sense to assume that “evil magic turns a spellcaster’s aura poison green” was something that had never happened in Equestria before it happened to Rarity in Inspiration Manifestation than it does to assume that Bon Bon had the first toilet in Equestrian history installed moments before Discord sneezed her house away in Three’s A Crowd.  

@TexasUberAlles
 
ex post facto doesn’t count. you have to interpret the text based on what preceded it, not what followed.

@Lucky Shot  
her aura was still a distinctive poison green  
It was poison green to us, but how do we know that it appeared that way to anypony in-universe? Like you say, how would you explain an invisible condition to a kid within 1 second? The audience is supposed to immediately know that Fakedance is evil, but the context of the episode is pretty clear that nopony in-universe besides Twilight did; regardless, unless/until the show addresses the matter of magical aura onscreen, supposition in either direction is still just supposition.
 
and her deduction is that Cadance has turned evil, not that Cadance is being impersonated  
If she could see that Cadance’s aura was the wrong color– whether because auras are universally visible or because her personal connection to Cadance (and previous distance from Chrysalis’s glamours) allowed her to see through any aura coloration disguise– it’s entirely possible that “Cadance has Face/Heel Turned” was a perfectly reasonable conclusion for her to reach; it’s ex post facto precedent for something that happened in Season 2, but having a poison green aura has been established as a visual indicator that a magic user has turned coat.  

@Princess Trixie vi Equestria
 
She’s a waifu, I’m sure she’ll be back.
 
Again.

It’s been four months but I have a few things to address.
 
 
@TexasUberAlles
 
Except that Chrysalis did not account for aura color; her aura was still a distinctive poison green while she was impersonating Cadance, who has a gentler cyan aura. Twilight Sparkle, magical genius nonpareil and audience of Cadance’s lovey-dovey magic during the foalsitting years, personally witnesses Chrysalis’s magic – and her deduction is that Cadance has turned evil, not that Cadance is being impersonated.
 
Twilight even tries to murder her when she sees the real Cadance, the thought of two Cadances never having occurred to her until that moment.
 
If Twilight had been able to see aura color, she would have noticed it was the wrong one. So would Celestia or anyone else who knew Cadance more than passingly, for that matter.
 
 
@Goobington
 
I don’t need to say a word to feel smarter than these kinds of people.
 
 
@TexasUberAlles
 
Well of course Rarity would notice that her own magic wasn’t behaving properly, regardless of whether she knew what color it was or not. The aura color fizzles so that the viewer immediately understands this. How would you explain an invisible condition to a kid within 1 second?
 
Does Sweetie Belle actually go through the motions of “figuring out” that there’s magic in that scene, or does she simply know / immediately accuse her? Because Sweetie is super-savvy to Rarity’s nonsense; she doesn’t need to see or feel magic to know her sister’s being sneaky. Rarity has one of the worst poker faces in the show.

I just wish Trixie wasn’t so forgotten

Technically they never contradicted this in anyway. They didn’t show Starlight parents or even said anything about them. They didn’t name where she lived and nothing said the flashback had to take place in Twilight’s past…
 
Not holding my breath this theory is ever used, just an observation.

@SeraphimDawn  

@Background Pony #2B3B  
Implied magical lesbian spawn? I’ll pass.

It’s more like a Twilight sunset shimmer

@Ajedi32  
The most obvious explanation for all of that is that it just never occurred to the writers or animators to have any of the characters comment on such things, and I think that actually makes sense in-universe as well as metatextually; Unicorns using magic to do basic tasks is such a mundane and universal thing that it would be like noticing and commenting on which hand someone uses to pick up their drink or which pocket they keep their money in. It’s not completely invisible, but the action itself is so much a part of the background chatter of daily life that most people wouldn’t even notice it at all, and those who do might be doing so on such a subconscious level that they wouldn’t automatically be able to articulate what exactly seemed off to them.
 
Rarity certainly seemed to be able to see that her aura was malfunctioning in Princess Twilight Sparkle Pt. 1:  

 
And Sweetie could tell that she was using magic to hide something behind her back in Ponyville Confidential:  

Ooooh, this is such a cool idea. I like it.

@TexasUberAlles
 

 
I’d argue there’s nothing in the show to suggest that the characters can se a Unicorn’s magical aura either.
 
Furthermore, there actually is evidence to suggest they can’t. For one, AFAIK nopony’s ever mentioned a unicorn’s magic color, even when it’s relevant. In addition to the obvious example of Chrysalis, nopony mentioned how Trixie’s aura color changed in Magic Duel, or Rarity’s in Inspiration Manifestation. Furthermore, Pinkie failed to notice that magic was even used to pull down the curtains in MMMystery on the Friendship Express, and it wasn’t immediately obvious to anypony that Twilight was using magic to manipulate the plow in Winter Wrap Up, despite the massive glowing magical aura around the entire cart.

@Lucky Shot  
Well, the important thing is that you feel smarter than the people who come up with these theories.

@Lucky Shot  
none of the characters in the show actually have or can see magic color or else Chrysalis would have been caught impersonating Cadance within minutes  
I agree that getting worked up about this whole thing is kinda silly, but there hasn’t been anything in the show to suggest that the characters can’t see a Unicorn’s magic aura. With Chrysalis, Occam’s Razor tells us that if her disguise glamours were on point enough to fool Shining Armor, Twilight Velvet and Night Light, Celestia, et cetera at close range, they were probably inclusive enough to account for aura color as well.

None of this retarded argument looking for excuses to make Starlight related to Twilight actually matters because this moronic brony theory just like every other moronic brony theory bases itself on an obtuse color relationship that isn’t even there and would mean nothing if it was
 
TWILIGHT SPARKLE | SUNSET SHIMMER | STARLIGHT GLIMMER are all unsubtle variations of the same basic name, they are inversions and foils to one another, all three of them also have similar godly powers related to harmony or cutie marks, all three of them have multi-colored / striped hair
 
Cadance has three hair colors, the chances of any one of them matching a given pony are astronomical, the yellow in her hair sorta matches Sunset’s, is Sunset related to Twilight? Only in literary terms, as she is a foil to Twilight, she is the Twilight that failed
 
“Magic color” doesn’t matter because magic color isn’t real, it’s only a visual guide for the audience, none of the characters in the show actually have or can see magic color or else Chrysalis would have been caught impersonating Cadance within minutes
 
It will always baffle me how strongly people clutch at straws to make retarded conspiracy theories, is it really that important to feel smarter than the government / your peers / anyone else who could not give less of a shit how good you were at wild guessing games

@RighteousIndignayshun  
Really? You can’t conceive any possible way for a unicorn to find a time travel spell without the help of their parents? Trixie found the Alicorn Amulet in a curio shop, and Spike found the cursed book in the ruins of the Ancient Castle of the Royal Pony Sisters. Hell, the remains of the Elements of Harmony were just lying around in the same castle. It is well within the realm of possibility for her to find a time travel spell.

@Goobington  
If that actually happens, I’m betting my bottom dollar on it being a rename or something. Maybe it’s something like Tangled where the child is stolen from the parents after her birth and…wait, no, then how would she have gotten to the past? There’s really just too many holes in this theory to really make it definitive, like Discord being Star Swirl.

@Jades  
Maybe they know about Starlight Glimmer, but don’t know that the foal Cadence is pregnant with will become Starlight Glimmer. Because she hasn’t been born yet.

@Goobington
 
And pray tell why don’t they know about Starlight Glimmer. That sounds oddly contrived. Could it be that perhaps no one told them about her despite them appearing in Canterlot outside the episode.

@Jades  
Twilight: “There’s this pony named Starlight Glimmer who has the power to steal cutie marks and looks like <Starlight Glimmer’s appearance>.”
 
Cadence: “Wow. That sounds exactly like the child we have in the future. Whose name we may not have chosen yet and whom we know nothing about, because we’re still in the present.”

@Goobington
 
That’s oddly convenient for this “theory” to work especially when the Mane 6 has met Cadence and Shining Armor multiple times after the premiere.

@Jades
 
This happens every goddamned year.  
“This is gonna be a Sue.”  
“That’s going to ruin everything.”  
“Based on the extremely limited info I have, I see no way that this can be done well.”
 
If having the forethought to go by a different name when you go back in time is enough to make a character a Sue… Then that matches up perfectly with how easily people will label things Sues.
 
Keep in mind that we still don’t actually know how pony names are chosen. Considering a pony’s name somehow near-perfectly compliments their appearance, personality, and cutie mark, it’s entirely possible that the name Starlight Glimmer will be chosen at Cadence and Shining’s foal shower.
 
It’s also possible that not all the information reached the Royal Couple all the way out in the frozen north. Besides, they have the Crystal Empire to oversee, and they can’t always be aware of every little thing that goes on miles away.