Did you do this all from scratch or??
It's amazing! I think the only thing I'd change is the color of the bonnet and how the inside ear looks. When it's in an ear bonnet, there should be fabric fully covering the ear and it's kind of looking shredded?
The ankle of the rider looks just a little too narrow in comparison to her thigh. It could just be the angle though.
I'd add a little highlight on the tail since right now it's blending too much with the outside hind's shadow.
Where is the noseband?
Obviously those are little changes, because like I said..it's gorgeous! What a thoughtful gift :)
"Strength is the ability to use a muscle without tension"