UTI In 15 month old baby. And asked!

My daughter who is 1 year and 3 months old, had 3 repeated UTI’s in the last 3 urine and culture tests. There were no symptoms like fever or irritation during urination in the last 2 episodes, however the report shown infection.   Last time doctor had advised us to give plenty of fluids ( water ) and we taken it very seriously and gave a lot of water from this afternoon.  Because of that she is urinating once in every 30 minutes . Is this because of water we give to her or any other issues. During the 1st episode of UTI, doctor had asked us to take an Ultra Sound Scan and the scan came out very nomal. They had recommended for Antibiotics for 14 days and asked us to take urine routine and culture but still the report shown as Bacteria (E-Coli) infection.  He again asked us to repeate the antibiotis for another 10 days and asked us to repeat Urine test and culture and again it had shown Bacteria (klebsiella oxytoca ) Infection. Hence they asked us to take MCUG scan this time and asked