While this is coming from an embaressing part of my life of which I try to forget and rather not talk about, when I watched the show I remember the first character's name was originally Ditzy Doo, but her name was mostly only known to the show's developers and hardcore fagsfans. When she became popular, they changed Ditzy Doo's official name to the fan name, Derpy. It's possible, but admittedly unlikely, that that was made before the change.
Your a month late. But yeah I think your right. Then they shoehorned derpy into every episode because fans wanted them too. then fans got pissed off because derpy was being shoehorned via their request.
These seem like a good start but there are a few discrepancies:
I am just going to say it, I doubt that "Ditzy Doo" would have a 10 INT, 14 Wis, or 11 STR. Pegasi have 4d10+12 HP, and have a ground speed of 60'( fly speed of 120'). However, this is in PF rules so YMMV.
Twilight Sparkle:
I think an elf would be closer to a Unicorn than a Human. According to PF Bestiary 1, she would need to have the Improved Familiar Feat in order to have a pseudodragon as her familiar.