Ok, so this idea came to me after reading a few Equestrian Girls Annon-A-Miss fics. I'm not saying this is a theory, this is just an idea I had that I thought would be an interesting premise for a story. I have no doubt that this idea wouldn't hold water as an actual conspiracy, but I do think it would work as a fan fiction.

So, we all know that Celestia never mentioned Sunset to Twilight, and we're all left to assume that after Sunset leapt through the mirror Celestia tried to chase after her and failed. Now, we know that there's a counterpart for everyone in the Equestria Girls world except for one character that we never see, the original Sunset Shimmer from the human world. I've read a few fics that explained this away with Human Sunset being in another state, being a traveling musician, and even a few where she was dead when pony Sunset took her place. What if Human Sunset went to Equestria after Pony Sunset went through the mirror.

Imagine, if you would, that her human counter part took her place as Celestia's exiled student, completely lost in a strange world that defies all sense of reality. She calls out for help, explaining that she was trapped in the fictional body of a unicorn only to be looked at with concerned eyes that silently ask, "Is there a problem with her brain?" Of course, Human Sunset would come before Luna returned from the moon, so there's assumably no one who can verify his past, leading her to be taken to a mental institute as the doctors "treat" her "delusions." Celestia soon catches wind of this and ends up blaming herself for the mental state of her student, believing that Sunset allowed her mind to create a fantasy world of bipedal apes for her shattered hopes to rest. Human Sunset is treated for years in the facility, slowly questioning if the many doctors were right about earth and humanity being a figment of her imagination.

Years later, Sunset is released from this facility with a clean bill of health, prepared to start up her life in Equestria as she continues to deny her memories of Earth. That is, until Celestia catches wind of Twilight's escapades in the human world. Quickly placing the pieces together, Celestia feels burdened by the guilt of not being there for the Sunset who went to the mental facility, and now weighs her options of how to move forward. On one hand, she could allow Sunset to continue living with the new delusion that she had been a unicorn her whole life, or tell her the truth and shatter her fragile sense of reality yet again. Sunset, (pony who went to earth) in turn, begins to also feel guilty for the original Sunset's mental condition, believing that if she had never went through the mirror that her counterpart would either never fall into Equestrian, or that her claims to being from another world would be taken more seriously.

Wow... that's dark. Go for it, could make for an interesting story.

I'd like to see this