Also, somewhat related, well... This will sound strange, BUT.
Until it's cleared up, if you can, take her off tap water, even if yours is filtered. Buy the cheap gallons of distilled water at the store and have her drink that instead. I had cats that had constant UTIs until I had a vet (at least the fourth one!) have me do that to start, and it cleared it right up.
So as a human veteran of bladder and kidney infections, when I got my next UTI, I took the same advice, and it seemed to help a bit. Since then, I find if one's nagging me, if I switch to cheap distilled water for a week and it seems to help me out a bit. Granted, my system isn't nearly as sensitive as my cats' were, but even if it's just a bit of psychosomatic relief--it's still relief, and it cost less than three bucks!
I do hope she feels much better soon. UTIs can be miserable things to have, be it pain or just that constant feeling of, "I think I have to pee, but I'm not really sure."