First thing to rule is her health. Maybe a trip to the vet to make sure there are no underlying health issues. If there is nothing physically wrong then you can start checking out her environment. Made any major changes lately? These little ones......who knows what goes through their little mines.
I know my little one will stop using the pee pad if there are more then two spots on it or if it its a few inches from where it should be. Yes......she is that anal