I gave my pup the ( Rite Aid ) Cranberry supplement 425 mg tablets (no artificial flavor or colors) ....one in the morning and one in the evening until she had her first heat. She never had a UTI and her vulva corrected itself after the heat.
There is a new procedure that vets are testing out for puppies with inverted vulva's. They are tacking it with a stitch similar to how they tack eyes in some breeds. Initial results have been quite favorable.
You may want to discuss that option with them. It was a big topic of discussion at one of the Repo vet seminars in the fall. My vet was at the seminar and was going to test it out.
I have a half-inverted vulva on a puppy right now - I'll probably hang on to her myself anyway, but how do they keep a puppy from licking at a stitch on their little vulva? I'd think they'd not leave it alone?
I have had good success with crancaps for RV pups so I would not do this tacking procedure unless I could not keep the pup UTI free without antibiotics. JMO