Has she been spayed?
If not it's possible there's a womb problem.
Or it could be a side effect of the medicine she is on. I'm sorry, but I don't know anything about Proin. Maybe someone else will post here who has experience of this medicine. Or you could ask the vet about the possible side effects.
But it probably is, like you say, a UTI. It seems that there's a tendency for these to recur. But it could be caused by something else: stones, for example, or a tumor in the bladder. (not necessarily cancer) Even a benign tumor could cause some irritation.
I wonder if your vet could perform an ultrasound?
Rawhide can cause problems -certainly. But I doubt if it would cause bladder problems.
(I started a thread about that, it's on this page) Rawhide's dangers are, choking, possible salmonella infection (which would be likely to cause vomiting and diarrhea, not, I don't think, bladder infection) -and damage to esophagus or gut blockages if large pieces are swallowed.
Last night I looked up all the possibles on the fourm what others had posted. It seems that it must be another UTI. One vet I took her to did x-rays, and some other test and found nothing the last time she went through this. She is fixed. I read on here of one case where the vet suggested keeping the dog on antibiotics for 8 weeks. I wanted to do that the last time but the vet said it had cleared up after one round. So, I really don't know if there is more that I or the vet can do. Wonder what others have done or other vets can suggest as well. I upped her cranberry pills the past two days. This causes her stools to be runny, of course that could be an issue as well. Her cleaning herself of runny stools, then the bacteria getting into the area where her urine come out,then the bacteria from the stools runs it's course, hence another UTI....yeah, I have been learning WAY too much about pet care ...lol
Cranberry pills can only help with the pain of a UTI by sweeping the byproducts of the infection out of the urinary tract. It will not treat the actual infection. Urinary tract infections can be terribly difficult to treat for any animal, be it human, canine or anything else. All it takes is one little bacterium to survive treatment and the infection comes right back. That's one reason it's so important to take all antibiotics until they're gone.
If it's been quite a while since the last round of x-rays, you might ask for another one to see if your girl has developed bladder or kidney stones. They may have been present previously but not large enough to see. Since UTIs have been a life-long problem for her, I think it's worthwhile to do some more in-depth testing to figure out why it keeps coming back. Have you paid much attention to how much water your dog drinks? Some dogs simply don't stay well-hydrated which can increase the possibility of kidney stones and other urinary tract problems. Wouldn't it be nice if it were something that simple? LOL!
I doubt the rawhides have anything to do with the UTI, but they should be avoided in a dog with chronic pancreatitis due to the fat content. Definitely check with your vet on that question. Dogs, like humans, need a certain amount of fat for good nutrition, but sudden spikes in fat can bring on an acute case of pancreatitis - particularly in a dog who has already had it. Chronic pancreatitis is darned difficult to manage in humans as well as dogs.
Please post back and let us know what your vet has to say about the urine sample and your dog's general condition. Having had a couple of UTIs in my life, I always cringe when I hear about anyone - or any animal for that matter - with one. Very ouchy!