My gf has had more than 10 urinary infections per year for 11 years. after each treatment, she gets candidiasis. what could be causing the infections?

From antibiotics: She should see a urologist to look at ways to see why she has such frequent uti. It could be from bladder stones, from bladder diverticulum, from sex, or other reasons. More than likely the fungal infection (candidiasis) is due to the effect of the antibiotics she is taking for UTI on the bacterial flora of the vagina, allowing overgrowth of yeast. She might try taking a different antibiotics.