One reason that girls with CAH can be susceptible to UTI’s is if they have ambiguous genitalia then often/typically the vagina connects into the urethra. Urine can then backwash into the the vagina and uterus.

My CAH-daughter is 5 and hasn’t yet had her vaginoplasty. Repeated UTI’s would be a reason to have the surgery now as opposed to later.

Maybe others can give some additional info.

Janet