Is it safe to give my dog a cranberry suppliment capsule?

I am currently using cranberry capsules for my dogs urinary tract infection. She gest repeated infections and I always start with the cranberry before the vet as oftentimes it will clear it up. My dog is about 18 pounds and I put half a capsule (500 mg, so 250 for breakfast and 250 for supper) in her morning food and half a capsule in her evening food. I also make her food like soup by adding at least a cup of water because you also want to help flush the system. If it does not seem to be working for my dog after 2 days, I bring her to the vet for antibiotics.