We Have A Female Dog We Found On The Side

We have a female dog we found on the side of the road. We came to find that she had two large stones in her bladder which we had removed surgically. Do I have to feed her the SO dog food the rest of her life? I do not know what kind of stones they were because it was too expensive to send them off to the lab. The stones were large, smooth and oval. Her surgery alone was over $600.00.