In little girls who develop UTI at a later age (meaning not since infancy), we think of two common scenarios:

1- Hygiene issues: contracting bacteria from unclean toilet seats, or inappropriate personal hygiene measures. What happens is that sometimes little girls use the toilet paper the wrong way, so they proceed from behind forwards, which brings the bacteria found in the stools into the front. These bacteria can migrate upward and cause UTI. 

2- Chronic constipation: in these cases, the stools accumulate in the colon, leading to what we call fecal overload. The colon thus becomes distended, and pushes against the urinary bladder. As a result, the urine inside the bladder becomes stagnant (the term is urinary stasis), which makes it a good medium for bacteria to overgrow and multiply, leading to UTI.

Your daughter's pediatrician will have to investigate the possible causes of her UTI and provide the right advice depending on the case.