This is absolutely adorable, and very fitting for the character. The water-coloring on her mane is very silky and mellow, and I like it. I could just pick her up and cuddle her. The little -squeak- on the right made me smile.
One thing I'd work on though, is line quality and diversity. I can tell that this was more of a leisurely drawing, but the lines are rather...messy. Not that it's necessarily a bad thing, but it can sometimes distract from an otherwise adorable picture. Also, (forgive me for sounding like a elementary school teacher here), be careful about coloring in the lines and everything. The color is starting to bleed outside near Fluttershy's bottom and legs. The more cleaned a picture like this looks, the better.