We always knew that. She's super organized (as seen in Party Pooped) and remembers the smallest details like knowing how many days it is to someone's birthday (think of that. Think of someone closely related to you whose birthday you know and without looking, and only a few seconds to do the math, tell me how many days it will be until then. Can you? Now imagine being able to do that for anyone, having made a note of when their birthday was who-knows-how-long ago?) and she was also the only one who could explain Twilight's machine for returning to the EQG world.



I'd say Pinkie is the smartest pony in any room that does not contain Twilight. It just goes unnoticed because she's hanging with the one pony smarter than her and her crazy personality makes everyone (in and out of universe) underestimate her.