A "sideways" seat probably means Amanda is riding sidesaddle (sela de amazona). In this arrangement, a woman's legs are placed on the same side of the horse, rather than having her straddle the horse (one leg on each side). Straddling the horse has been considered unladylike. A basket seat probably means it is a woven wicker construction, rather than leather. With the footrest, this is a picture of a very dainty riding apparatus, designed for style and fashion, rather than usefulness or speed