sorry to hear about the relapse and the lack of proper diagnosis the first time, but from personal experience, the new diet shoud do the trick!!! I had at least 4 different cats with 4 different stages of the UTI (one with bladder stones ) before I put the ENTIRE gang on Hill'sPrescription c/d food. Never even a hint of a problem since then.
p.s. I also use bottled water to cut down on the possibilities of minerals in the tap water.