Hmmm, unfortunately presence of leukocytes alone is not indicator of kidney infection. A common cold will cause leukocytes in urine. It has to be taken in context of a) concentration of Leu, b) presence of blood and protein c) presence of nitrates, plus fever and maybe a continuous ache in kidney.
She could just still have population of the bladder, which should not necessarily be treated in absence of fever. When kindey is uder attack it tends to let blood (and protein) pass – if these are not present then it indicated a lower urinary only.
Also, did the doc send the urine sample he dipped off for culture? And, did he check what was cultured last time to be sure that it want resistant to the antiB he just prescribed?
However, its not uncommon for an opportunisitc secondary colonisation, and another course of antiB shouldnt do any harm – its just that after 5 yrs of managing chronic urinary condition in my daughter bitter experience has taughts that you need to understand & validate proposed treatment.