This is the odd result of having Epona push against an Armos Statue. You may remember that Armos pose as statues, but come to life when you grab at or hit them. Armos statues are actual statues in the shape of Armos, and you can push or pull them to solve puzzles. If you move Epona toward an Armos statue and try to push it with her body, this will happen. She will get stuck at an odd angle until you back up. If you hop off of the saddle, you can get a good look. Epona is not stuck like this permanently, because if you hop back onto her and walk backward, she will become angled properly on the ground again.