Saddles are hard to draw, so, hey, I found a way to draw somebody riding … something in a way that suggests a saddle (or some kind of tack) without having to draw anything. Plus I think her pose is cute with the way you see the soles of her sneakers. I actually penciled some designs on them to represent the waffle patterns found on actual sneakers, but I ended up erasing them out. They sort of blended in with the detailing on the straps across the … something’s chest, where now the simple outlines and white forms make a contrast. Or that is the idea, anyway.
I don’t know what the something is, but it’s definitely older and wiser than the person riding it. Maybe this is one of those fantasy situations where the being being ridden is fully sentient and is acting as a tutor or mentor to its rider. That would explain the lack of a bridle or stirrups– you wouldn’t dare drag your respected teacher around by the nose, and you only stay on his or her back as long as he or she wants you to!