Reoccuring UTIs

Dakota is almost 5 months old. She had a UTI at 16 weeks. The vet gave her a 2 week supply of medication. We used it all and then 3 days after the mediciation she showed signs again of a UTI. We took her in and the vet did a bladder sample. And it came back negative, but was noticed that Dakota has an inverted vulva. So they are not sure if they infection was internal or external because of the vulva and we were just getting false positives. So we were taking Dakota on vacation, so they gave us round 2 of medication and told us to see how she is afterwards. I work at a college and the vet program director told me that with the inverted vulva to try to do something to prevent UTIs until she goes into heat. Her suggestion was cranberry juice. So I bought it and started to think about it. Dakota drinks tons of water and I wasn't sure about giving her lots of cranberry juice. So I spoke to our breeder last night and she said to give Dakota cranberry vitamins. So I went to the store looking this morning and most are 450 mg and say to give 2-3 tablets a day. I don't want to make Dakota worse, but I also don't want her to continue to have UTIs until her first heat cycle to see if this fixes the problem or not. So anyone have suggestions that have been in my place before. Money is not the problem here, I will do what is best for her, I am just not sure what that is.