It makes sense if she isn't eating much, then she wouldn't be pooping much either. What goes in , comes out. I wouldn't let her go without eating for too much longer though, without getting her checked out. Where did you get her from? A breeder or someone privately, as she is already 5 months old. You can call up the previous owners and ask them what her eating habits were before you got her. Maybe she is just adjusting to her new home and surroundings, but because she is still a puppy, she should be eating 1/3 of a cup 3 times a day.