Meant to post this earlier but got interrupted at work - sorry. I sympathise enormously with your D - I am very prone to UTIs and they are awful.
I have some ideas for managing symptoms if your GPs haven't been too helpful...
First thing is, if she is really prone (and my limited understanding is, once you are prone, you can get scarring which can make you more prone IYSWIM) then it's a good idea to have some sample jars AND a supply of ABs at home. This way, at first symptoms, you can take a clean sample but give that first dose. My UTIs go from twinge to agony in about 2 hours so I have to take the ABs immediately. I always have a couple of Cephalexin at home for this - which my GP willingly overprescribes.
I also have ibuprofen and co-codamol but not sure what kids could take (Medised?)
At first symptoms, it is really important to drink lots of water in the first hour or two - half pint every half hour. Some suggest adding a bit of bicarb of soda or cystitis salts to the first pint but I've never found these make a different. Lemon barley water is also believed by some to make the wee less acidic. you would need to discuss with GP what is OK for kids...
After the first couple of hours, she needs to drink a little every hour or two.
Emptying bladder fully is really important and this is really difficult as it is so painful and in spasm. Using a gentle shower downward (or bottle of warm water) over the vulva or getting her to wee in the bath will help.
While things are not too painful, tipping the bladder is helpful - when finished weeing, count to 20 tip forwards to tilt pelvis, squeeze a bit more wee out. Do this backwards too and left and right.
Hot water bottle might soothe things too.
I hope she is feeling better once the ABs kick in.