Causes of bladdar infection: infrequent urination, holding urine, poor hygine, wiping back to front, frequent sex, dehydration and I am sure there are others. I used to get them frequently when I was in 4th grade as my teacher would not let us go to the bathroom. (terrible right) I finally got permission from the PRINCIPAL to get up and leave when I needed to, which was not often. Then I had a time right after I got married. ;0) had to go to the doc and get a antibiotic on my honeymoon. fun.
I have learned that once you get a bladder infection or UTI that the bacteria never leaves your body. So you must stay hydrated. always wipe front to back. You are supposed to go pee before AND after sex (how romantic) Although I could never do both. Cleaning with any thing down there other than MILD soap and luke warm water can make matters worse. Especially around her monthly she should take extra caution cleaning up. Possibly using a luke warm wash cloth when she goes potty. Cranberry juice and supplements may help. Make sure it is not cranberry juice cocktail because it is mostly sugar and wont help. Be careful about using too much cranberry or other acidic products because they can burn the lining of the GI an Urinary tract if you consume too much (which would be a lot, but it happens). I hope she feels better soon.