Just a thought but it sounds like you are using the "litter box" approach - I think the terrier breed is known for digging so perhaps she enjoys playing (digging) a little too much. You may need to try something different as far as housebreaking technique. I have seen quite a few links discussing the fact that their dogs are doing the same thing. Perhaps you can do a history search and find additional information. I know with one of our dogs who did the same thing, we constantly were watching over our shoulders to pick up anything as quickly as it fell or she would also feel the need to scatter it around. Best of luck to you!
__________________  Tracy and my  S 
" If a dog will not come to you after having looked you in the face, you should go home and examine your conscience."- Woodrow Wilson |