There may be many causes for E. coli infection in the urine. It could be due to bad local hygiene with ascending urine infection. More importantly it could also be due to an internal tendency of the urinary tract which predisposes the child to have repeated urine infections, for which we need to do certain investigations like ultrasound and MCU. Right now you need to treat her with antibiotics and then do other investigations. I am sure your paediatrician will be able to help you.