one more thing that makes it easy to litter train kittens and cats is that they possess an instinct to bury their waste. this is a behavior passed down from a time before they were domesticated. they would bury their waste to hide their trail from predators. they also do it for hygiene reasons, simply that poop stinks..
that's why cat owners may occasionally find "deposits" in indoor potted plants
if a cat is not using the litter box set out for her, there must be something about it the cat does not like.. the texture or smell of the litter, the location of the litterbox, the type of litterbox... etc.. some cats won't share litterboxes with other cats.