no idea on the treatment route but if you haven’t already done so, get a sample from her. A shallow take away tub usually work if she’ll let you scoot it under her as she goes. Is she teeny tiny? A lid might be better then pour into something else!
In my experience, if it is a UTI, it won't clear up without a course of antibiotics. The urine sample will tell your vet everything he / she needs to know though.
There are things you can do however to help with reoccurrence. Keeping the urine acidic helps - vitamin C or cranberry, just the same as ladies with cystitis!!
My girlie has very bad spay incontinence and had repeated UTIs, until we got her medication sorted. She had to have antibiotics every time to clear the infection.
I use cystophan to help prevent uti in a particular cat. It really works, I just sprinkle the capsule into food.
Another one, male, has the special food and cystophan. He has about 1 attack a year now compared to the 2 a month he used to have.