It's actually supposed to be Surprise, Pinkie's "beta" variant. Back before G4 was finished, the "mane" cast was comprised of different characters - instead of Twilight, Pinkie, Rarity, Rainbow, Fluttershy, and Applejack (in that order), the characters were Twilight (not Twilight Sparkle), Surprise, Sparkler, Firefly, Posey, and Applejack.
Oh, certainly. I'm quite familiar with (your? Almost certain it's yours - I distinctly recall reading it somewhere, but nobody's memory is 100% reliable) Ask-Surprise Tumblr; I've been watching it for updates like a hawk. I was just explaining Surprise's relevance to G4.
(As an aside, assuming it's yours, keep up the good work with Ask-Surprise!)