You do the adorable SO WELL! If I ever have children, I hope they can be as cute as your drawing here, because that would just be too perfect.
However... As adorable and worthy as this is, it is really out of character for Fluttershy. The disheveled mane, the awkward smile, the braces... Well, I guess I could see the braces, but Fluttershy has always given me the impression that she was raised by stiff-lipped, rich ponies. When she is awkward, she hides her face, and her mane is never out of order, even when she was a little foal. If I could change anything about the picture, however, it would not be to straighten up her mane and soften her smile, I would change the character depicted to AJ. You do such a beautiful job of the tangled mane that I couldn't bring myself to tell you to change it, just who you put it on. AJ would absolutely be in this sort of state when she was a teen filly. Hastily gathered and restrained hair, trying to smile naturally for the cute, popular colt that is standing just a few feet away, flashing those great oral metallics that Granny Smith saved up for 2 years to afford... That would absolutely make this picture perfect.
I think this picture is beautiful but I do have a couple of things to say about this!
The eyes are really beautiful even the shade has a really good shine into it. The braces are really good and super shiny and it actually look like real braces but the teeth does not really look like fluttershy because fluttershy is suppose to be shy, right but the hair could be more better because the hair is all curly like and fluttershy is suppose to have straight and the top and then it gets curly at the bottom. Fluttershy, I think she is not suppose to have freckles to me because it just does not fit on her but I love how you did the art and everything and when I get older I hope I could be an wonderful artist like you.