Hi and welcome to PT. You might want to move this to the dog section.

My dog Jimmy was diagnosed with a UTI a couple of months ago. The antibiotics weren't working and then the doctor thought it was his prostate. X-rays showed it wasn't overly swollen. He had sandy sediment and kidney stones that weren't showing up on the x-rays. When he couldn't pee I would rush him in and they would put a catheter in and it would push the sediment back up and Jimmy could pee normally, but this was just a temporary fix. Dogs don't pass stones like humans. Finally one morning he couldn't pee at all. Zero. The vet gave him emergency bladder surgery and removed 8 large stones! I saw them and they would have been near impossible, if possible at all, for even a human to pass. He got his stitches out yesterday and we are still waiting on the stone analysis.

It's possible your dog has been misdiagnosed just like Jimmy. Females don't have a prostate, so that is out as a problem, but they can get stones. Maybe ask your vet if it's possible.