Was there a CLEAN litter box available for the kitten to use, in a place that she would feel safe? Have you dewormed her and gotten her all of her age appropriate shots and medicines? Did her diet suddenly change types of food? Is she spending large chunks of time alone? Cats usually do thing like this as a result of something not being right with them, their environment, or their diet. If you received your kitten while they were too young to be away from mom, or they were otherwise separated from mom at a young age, they may not know what a litter box is for just yet. You may have to teach them, but usually the desire to keep their home tidy by burying their poo takes care of that.

Depending on how old the cat is, you may want to get her checked out. It's not usual for cats who are litter box trained to go outside. Also a dirty box or a change of litter could be the cause.

Cat shit is the worst to clean up afterwards