Technically true, but it doesn’t hold up to scrutiny, regarding security or lack thereof. That might be part of the joke. (Yes, even Star Swirl’s scroll probably wasn’t as well-guarded as it could’ve been)
 
She isn’t stupid though, so she probably could’ve contributed something in the planning process, if she were to play a bigger role in the episode.

@Jarkes  
Nobody would know. Nobody.  
“The last I saw him, when Ultron was sitting on him. Uh…yeah, he’ll be missed, that quick little bastard. I miss him already.”

I’ve been thinking about this and I actually think Starlight could pull this off.
 
Shining knew Twilight would recruit the rest of the mane 6 and Spike, but if Glimmy came in by herself pleading ignorance would he suspect her enough to stop her?
 
Also knowing spells that can duplicate objects, be in two places at once, and cloak herself I think she could do this.

@genervt
 

@Ekhidna  
And finally puts to rest that whole Twilight is Spikes mother idea.
 
Which is now blasted apart.
 
I take great joy in this.

THE FUCKING SCEPTER

Twilight really should have asked for her help if for no reason other than the fact that Shining Armor wouldn’t be expecting it.

@Vivace  
So she has experience breaking into Canterlot Castle.

@Vivace  
Um. She also broke into Canterlot Castle before to get the time travel spell.

Uh, Starlight. You broke into an unguarded castle that wasn’t fortified specifically to keep you out. I don’t think that would prepare you for this without inside help like Spike had.

Lol, Rainbow’s dress!

Starlight looks glorious

Twily really should have seen this coming.

@lance blazer  
Hellz yeah. One of my personal favorites now. Mainly because we have confirmed the sibling relationship between Twi, Shining, and Spike!

Yeah, but Twilight’s Castle was left unguarded…this one definitely wasn’t.

@Ekhidna  
did you like the episode?

Yeah, infiltrating an UNGUARDED UNDEFENDED castle was sooooo hard.
 
And about the changeling hive? That was mostly thanks to the others and Thorax most of all.

On the other hand, Twilight’s castle has zero security as far as we know. Or maybe the OP is talking about her stealing Starswirl’s time travel spell?

You know that’s a good point.