I think the coat is fine(I prefer it to the nearly ubiquitous sweater design), maybe change it's color to match the blue in her cutie mark, but other than that it's fine. The dress seems like it might be a bit short though.
Her arms look a little wonky, mostly her left forearm. It looks sort of stubby next to her right one.
I know she's supposed to have a buttload of hair, but I think it may be piled a bit too tall (especially with the birdnest on top). Maybe if you shortened it down a bit, her face would look a little less elongated, and she'd seem less "top heavy".
I think the sweater is a cute idea, but it seems a bit too thick on her shoulders. With both the thickness there and the added shrug motion, it makes her neck look really small.
Also wondering, where is the source of light for your shading supposed to be? It seems like it's coming from below on her left side, and from above on her right. This doesn't really have much of an impact, but I feel like due in part to this it's sort of hard to tell how turned her body is away from us (which may explain the aforementioned difference in arm length).
Otherwise, I think it's looking pretty good. I know nothing about art, but I hope that helped!
That pidgeon nomming her hair is best. As for suggestions... maybe remove the coat. She has that huge hair and in combination with the coat it just looks so "heavy" all in all. I like the color though, maybe turn it into a light little green jacket?
Hmm, in my opinion, I am not liking the big green coat she has, it doesn't seem particularly "Fluttershy". The dress however, looks absolutely perfect for her. If you don't like the look of her dress on the outside, then how about a coat of this design?[link] Also, as a suggestion, how would she look with a floppy sun hat like this? [link]
How about a yellow top and green/pink shorts/skirt? I've seen a couple of those and they look nice on her I'm not asking for a complete redo of this picture with this idea. Just a suggestion for the future.