How to treat chronic recurrent urinary tract infection?

my friend is suffering from chronic and recurrent UTI.she has already tried many times all conventional therapies including triple antibiotic regimen of trimethoprim sulfamethoxazole+nitrofurantoin+diproflo… to no relief.also she has practiced abstinence, and tried vitamin c and cranberry juice.plz help me treat my friend because all the doctors i go to advise me the same antibiotics which unfortunately are not helping and only giving side effects like nausea and vomitting.