Lots of water. Frequent baths and you can try cranberry juice or apple cider vinegar. The water keeps the urine flowing so that the bacteria can get flushed out. If you bathe him frequently, it helps keep the urethra clean. Cranberry juice increases acidity which decreases bacteria. You can try 1/2 teaspoon of apple cider vinegar in his food once a day to try and increase the acidity that way.
But, sadly when there is infection, you really are better off with getting an antibiotic. I am not a vet but these are some things that you can try.
Best of luck!
Friends will step in when the rest of the world steps out.
Since she already has the infection, I would go ahead and treat it with antibiotics. It is the best thing for her.
Once it is gone, then go natural to prevent the UTI from returning. There are some amazing products on the market now, and if you google cranberry power, you could find alot of useful info. Also look for a holistic vet in your area, they would be able to direct you to natural altrunatives to any problem she would encounter.