Maybe not.  
@MuttonBash  
“A Canterlot Wedding – Part 2”: After discovering Cadance’s dark secret, Twilight has to find a way to save her brother, the wedding, and all of Equestria.  
https://www.equestriadaily.com/2012/03/episode-synopsis-announcement-canterlot.html

@Background Pony #C565  
Kelpies are shape shifting Water Spirits

Don’t you guys read my stuff? Cozy Glow is Briar.
 
Yeah, remember Briar and Bramble? Turns out “keplies” are a race of beings Chrysalis created with her magic in lieu of the Changelings (since the Changelings are reformed).
 
Kelpies are able to assume any shape, replicate any power, and can fool most forms of detection (telepathy, omniscient, the security systems of the TARDIS).
 
The titular Mean Six are six kelpies. Briar, Bramble, Butcher, Bully, Brute and Beast.
 
So, Cozy Glow isn’t Chrysalis. Rather, she’s an agent of Chrysalis.

“I’ll create my own elements of harmony! With blackjack and hookers!”

@Background Pony #A12B  
Too bad it sacrificed Twilight’s character to do it.

What ever the Mlp staff is doing, they doing a great job for this episode making the fandom questioning weather Cozy glow is evil or nice, questioning what’s her motives but half of us already know because the leak happen.

It absolutely isn’t queen crystals. In the second part synopsis for the finale, it refers to her as “Cozy Glow” not chrystalis. If she was her, why would it not be revealed in part 1?

Which is totally why she cared so much about the CMC

@C.H  
How do we know; Who or What Cozy is until the end of the season? I’m betting on Chrysalis’s Daughter, She doesn’t look like a Pawn of Neighsay, but maybe Neighsay is a Pawn.

Your wrong, cozy glow is not chrysalis!