Dog wont potty in backyard just on walks, how can we fix this.?

We got a dog from a friend. The only way she will go potty is if we walk her. Is there any way to get her to go potty in the back yard like our other dog? We just don't have the time to walk her 3 to 4 times a day. We don't want to give her back to the people that had her, they mistreated her.