I really enjoy the choice of outfit here; the ruffly tutu reminds me of when little girls play dress up and play around, the necklace (I think I see a cupcake on it) is wonderful for Pinky because of her love of cupcakes, and the wig is exceptionally nice.
I also like that you have her cutie mark as a hairpin. My only issue is the expression, really. I think she could appear more excited when hopping like that.
Overall, however, very good.
...please disregard all of this if the critique was meant for the photography rather than the cosplay.
This shot is so incredibly clean, I am greatly impressed. The overall pink tone over green is very pretty!
Though, the opposite directions of the lighting is odd. The light coming from the cosplayer's lower left side, and from the upper right side in the background behind her doesn't look natural. I feel that the lighting should have matched the way the sky was lighting up the trees behind her. Or even just extra lighting on her right side so that she was totally illuminated.
My only other issue, which is something that probably couldn't have been prevented, is the necklace in her face. I'm not sure reattempting the photo would have done much better, but it does block her face from view. Because of who she's cosplaying, you should really aim to get that big smile in the picture, but with a shot like this, I can see that being difficult with her jewelry, so that's forgivable. :]
The only reason I give this a 3.5 for Originality is because jumping shots of Pinkie cosplayers seem to be rather common. While your shot is fantastic, it's not something unseen by cosplayers of this character.
However, this is an excellent shot. It fits the character cosplayed, the cosplayer is adorable, and it would be a great cosplay portfolio piece!