Potty Training Prairie Dog?

I have a juvenile female prairie dog. She was captured about 2 months ago and has been living in our house since then. She is very friendly and tame and is let out of her cage several times a day to run around the house. The only problem I have with her is potty training. I put a corner litter pan in her cage with about an inch of recycled litter and began picking up her droppings and placing them in the litter. She will occasionally use the litter pan when she is confined to her cage but when she is out she will urinate wherever she happens to be. The cage is at ground level and the door is left open when she is out. Does anyone have any suggestions on how to get her to use the litter pan? The droppings aren't that bad to pick up off the living room floor but I just can't have her urinating on our furniture.