[Gnarly]

Some hedgehogs will use a litter box, but they are the minority. Most will go on their wheels, many will go where ever they please and the remainder may go in a litter box.
If there is a corner, or area of the cage your hedgehog prefers to eliminate, place the litter box in that place, to encourage it's use.

Are you finding any feces at all in her cage? If so she is going in her cage.

Many hedgehogs will continue to eliminate on their human counter parts, it's a normal part of hedgehog life. While some grow out of this with age, or cut back, others will just go when and where they please. Keep extra paper towels on hand, and expect to get pooped on

 

[Gnarly]

Funny, I just received a hedgehog yesterday and put in her litter box last night. She's since, been using it - just as the hedgehog before her.

Lucky you.
Out of my eight hedgehogs, there is only one I would consider "litter trained". The rest will use the box, but also other parts of their cages, and their wheels.