If there is no improvement after 48-72 hrs of starting antibiotic, it should be changed. Even after receiving 8-9 days of antibiotic there is no improvement and her stool test
is still showing pus cells that is suggestive of persistent infection. So I would suggest you to consult your doctor as injectable antibiotic may be needed now. Give plenty of fluid to maintain hydration of the baby.
If oral intake is poor then intravenous fluid may also required.