Twilight’s overreacting, but I can kinda see why she might. Even if you don’t ship them, Sunset is the single most important person in Twilight’s life at his point. Starlight is from Equestria, Sunset’s old life and her “real home”. I can imagine her worrying that Starlight may try to take Sunset back with her, even if the chances of it actually happening are pretty slim. Sci-Twi’s insecurities still weigh fairly heavily on her, albeit not as heavily as they used to, and this definitely has the potential to make her neurotic if she lets it get into her head.

@Mystaldi 
is like lincoln clay in mafia III

@RushCars24 

 
Starlight’s smugness suggests she’s enjoying Twilight flipping out about it.

@RushCars24  

 
Sunset. : It’s like grumpy old men.

Also, I’m restoring the SciTwishimmer and Implied ShimmerGlimmer tropes, and would request to not remove them, as the artist states it’s a shipping picture, and at least partially romantic jealousy in the picture’s description - _SunLight will prevail - and SunLight is one name for the Sunset x Twilight ship.
 
At the very least, the change should be to Implied Scitwishimmer, not entire removal of the tag, I think…

“I don’t care who sent you! You’re not taking her back!”

LOL XD!

HOLY SHIT, YOOOOO…! This is so much perfect art accuracy and quality I’ve even seen, which had to dump many much of my upvotes in. My favorite! Like, what’s wrong with you, Twi? Everyone in your world doesn’t know Starlight Glimmer yet. Just chill out, will you? Even you already have six best friends, it’s still possible to add one more on your list.

Rarity : Alright, darling, what’s the meaning with this bad interruption? Is this some kind of-…
Sci-Twi : Y’all don’t know what’s going on here?! She took my best friend! ONE OF MY FUCKING BEST FRIENDS!!
Starlight Glimmer : The hell are you talking about, Twi?! This is just a visit, I’m not taking any of your friends!
Sci-Twi : NO! JUST FUCK OFF! Go back home to your current friends in that portal! You’re not necessary to be here!
Sunset Shimmer : Refrain your language, Twilight. Do you want to get carried away by the mall security?
Applejack : Yeah, Twilight! Lighten up, will ya’?
Rainbow Dash : I’d second that!
Pinkie Pie : Don’t do this at the newcomer’s face, Twilight!
Fluttershy : Buy her some time! She’s new around here!
Rarity : Don’t be such a ruffian, darling!
Juniper Montage : sighs and facepalm
Sci-Twi : I DON’T CARE! Me, the six of you, and Juniper will be MINE! That beanie freak ain’t welcome here!
Starlight Glimmer : Then how about I’ll throw something into your face, like you’re an UGLY BRAT!
Sci-Twi : Oh no, you don’t! If you want to pick a fist fight, then COME AT ME!
Sunset Shimmer : Okay, girls! Everyone! Calm down! What about we all nine girls here reconcile together?
Sci-Twi and Starlight Glimmer : SHUT UP, SUNSET!

apparently the artist didnt make the pic with shipping intentinons, so… bye tags

Defensive GF?

@angrybrony  
Well maybe keep that opinion to yourself and hide the ship in the filters, finally.

@DAPLR  
no, i just think it’s stupid.

@angrybrony  
Jealous it’s a popular ship now?  
Before long it’ll overtake Twixie, since Starlight and Trixie is actually a thing (actually friends)

@Background Pony #E928  
Well, Starlight and Sunset got close fast, but as as the artrist wrote under the pic - SunLight will prevail.

Starlight: She’s mine now, Twi~.

@DrakeyC  
Not everythig .. what about Trixie ?

Girls, girls! Remember: threesomes solve everything.