Okay, I have seen the original picture now, and have more input.

As well as the shape of the head that I mentioned before, both ears are facing forward in the original, so you need to fix he one on the right. For what the rest of the ears would look like size-wise, go to pet of the Day and search for horses, and I am sure you will find plenty of examples. The ears looks kinda small now.

Hair really isn't that hard, just think of it as "shading" but with long strokes. Nothing to be afraid of, okay?

I also hope there's more to the page, so her muzzle isn't right on the edge. I know it is in the original picture, but that's the advantage of an illustration, one can enhance reality!