The deisgn itself is quite beautiful and it's very appealing to the eye. However, more shading around the legs, face, mane, tail, knees, hooves and eyes would add more to this deign. And when I mean shading, I mean shadows. The appoloosa like spots on her back would look much better is they were blended in, like what you did with her foal design. More muscle detail around the face and eyes would also be good to show off her body and strength. Apart from that, the blending of the white and blue is beautiful and it's a very nice design.