Firstly, I'm going to repoint out the missing cutie mark. Not really your fault, but just to get it on here. Her face is a bit too human, especially the eyes, and the way you fit the hair with them. And, y'know, the whole body shape. Also, since when would she be out there without a scarf? Mittens? Socks?
Enough negativity. It really is a cute winter piece, and I love snow with a burning (or perhaps freezing) passion. My only suggestion is to make your ponies more pony and less human. Keep up the art, and don't let me discourage you.