Bladder and kidney stones are porous and bacteria living inside them are very safe from antibiotics. Of critical importance in treating struvite stones is an antibiotic sensitivity test of bacteria found in the dog's urine. Only in this way can we chose the proper antibiotic and the proper dose. The secret of success is to use the right antibiotic at a high enough dose for a long period of time. The antibiotic should be give for at least a month - better yet for one month after x-rays show no remaining stones.
Occasionally, bacterial infection is due to some anatomical defect causing urine pooling within the kidneys, ureters or bladder where bacteria can live. These defects are quite rare. They are either inherited defects or caused by prior surgery such as spaying. A contrast dye x-ray would detect such defects. Such a study would most likely be done if standard treatments fail. struvitestones
My vet mentioned the anatomical defect when Princess had UTI, I think it's worth investigating, for your pup. Was she spayed early?
Cathy (701Barney) used Uroeze, you can ask your vet about it, I think it needs a prescription.