The fact that Celestia treated Daybreaker’s taunts seriously rather than just laughing her off suggests Starlight Glimmer’s imagination struck a little too close to home. It’s pretty clear Daybreaker accurately depicted at least some small, unsettling part of Celestia’s psyche.

@BigRedJ  
Or the fact Daybreaker IS Celestia. It’s not like she was saying things only Celestia would know, just obvious things like Luna’s banishment.

Everyone is talking about this and all I wanted is to see what makes Celestia special.
 
Yeah… I wish the episode had made a clear effort to indicate this is the case. To me, Daybreaker is just SG’s headcanon until she actually exists.

Parroting some other comment I saw that said since Celestia was full of Luna’s dream magic she had the parts of her psyche she feared most project into the dream realm. Hence why Daybreaker talks like she knows Celestia so well.

I don’t think so. It seems out of character.
 
Perhaps she is afraid that ponies see her as such and fear her being royalty and all and this being a ponies dream so essencially a depiction of her  
or she is afraid of turning into something like this as well seeing as it happened to luna.  
It might even reinforce past trauma.

Deep shit