That's a great question. Have you spoken to your doctor?

That's so strange. I'm not sure if it's her diet But a gynecologist should help.
I'm confused as to why she's having this problem.

Not me, my niece has this issue of recurrence. Tried different doctors and medicines but still bothered by UTIs

Recurrent urinary tract infections (RUTIs) in women are mainly caused by reinfection from the same pathogen, most often E. coli, which originates from the rectal bacterial flora. Other risk factors for RUTIs include:
Frequent sexual intercourse
Spermicide use
New or multiple sex partners
Having a UTI before 15 years of age
Estrogen deficiency
Urinary retention
Incontinence
Genetic factors
Other factors that can place patients at risk of complicated UTIs include: Diabetes mellitus, Neurologic conditions, Chronic institutional residence, and Chronic indwelling urinary catheterization.
The most common way of dealing with recurrences is taking a low dose of one of the antibiotics used to treat UTI. However, bacteria may become resistant to an antibiotic overtime and it may not be effective in treating subsequent infections.
Some behavioral changes that may help prevent recurrent UTIs include: Drinking more fluids, Changing contraception, Voiding after intercourse, and Hygiene.