Hi,
One key point will be what kind of crystals (if she indeed is having crystals form ) - struvite or calcium oxalate. Though there is now a food to address both (I believe by Royal Canin), overall, I do think feeding a homemade diet (one that your vet approves as properly balanced - there are several books out there including a key one by Dr. Strombeck, on various homemade diets for various conditions - i.e. needing lower protein and/or lower phosphorous) or a good canned food, is the best way to go.
One key point will be what kind of crystals (if she indeed is having crystals form ) - struvite or calcium oxalate. Though there is now a food to address both (I believe by Royal Canin), overall, I do think feeding a homemade diet (one that your vet approves as properly balanced - there are several books out there including a key one by Dr. Strombeck, on various homemade diets for various conditions - i.e. needing lower protein and/or lower phosphorous) or a good canned food, is the best way to go.