Urinary Tract Infection. Hopeless.

My sister is getting recurrent UTI for the past 6 years(twice a year). She feels burning and pain in the Cervix and vagina(sometimes in urethra). There is urge of urination all the time and the pain becomes sharp at the time of urination. WE have consulted many doctors. The problem goes away after taking antibiotics but it comes back again after few months. CT Scan for KUB showed some minor issue with the urinary bladder and Culture of urine gives high count of Escherichia coli. When the infection is at peak, there is blood in the urine which varies from few drops to few ml. The antibiotics tried till now are nitrofurontoin, levofloxacin, amoxycilline and bactericin. She maintains proper hygiene. She was sexually inactive till last year and even after being sexually active he maintains proper hygiene but the infection is occurring again and again. Kindly suggest a solution. Really hopeless.