“Confusion Keeps Me From You” by xiao668
 
“You know dear, the world was finally right again a few weeks ago. Everything stopped being confusing and everything made sense again. The doctors even started making sense and let me and everyone out… then that rainbow came and the world was confusing again… But don’t worry, I’m sure the world won’t be confusing again really soon. If it could all make sense again once. I’m sure it’ll make sense again real soon dear. Then mommy will be back home.”  
-Reharmonized Ponies POV Rarity
 
A bit of a mix of fan art between Daddy Discord and Reharmonized Ponies (but mostly, Reharmonized Ponies).  
Honestly I’ve never read the fanfic but I follow the audio version on youtube.
 
I heard the common theory about her being Diamondtiara’s mother before but in all the picture’s it’s usually very cute looking like a normal pony family. The idea of her being her mother AND a nut case, BLEW. MY. MIND. So I combined my two favorite theories about her character.
 
I was kinda going to the very sweet and motherly Golden tiara with the expression, though I think it kinda ended up creepy…
 
My cute little filly’s growin’ up~