Try Ural. Yes, the package says not for under 7, but this is so parents don't just self treat. You have gotten a sample from her which is the main thing. (well that was the advice from the chemist I saw for DD2, who herself was also a mum)
Just double check with your chemist just to be sure yourself.

Pain relief of some kind may be beneficial as well and of course as much fluid as you can get her to have. Cranberry juice might be good as well.

Hope she gets better quickly for you. I still have bad memories from when DD2 had a UTI

ETA: Slow typing. Sorry your chemist said that she can't have it