The girl seems out of proportion. Her arms and legs seem too short. As others have already suggested, study references of people riding a llama.

Aww, that is such a cute idea and illustration :D I never thought about how to ride a lama but what caught my eye was the leg position. On a horse without saddle you would still have the leg at the sides not on the horse's shoulder. So i would assume that is the same with lamas. Maybe you find a reference picture if you want to check that out. Hope to see the colored version, too :)

It is showing your creativity. Nice

Nice drawing! If to say problem... maybe the arms and the hands are a bit out of proportion? Legs as well, but this could mean your caricaturization, and some of the wonkyness in the line art is due to the lack of illumination. You could do a few value and colour studies on top and find which one best presents the image before going final :D