My ginger cat was in at the vets for over a week as he had kidney and bladder problems, when he was a lot younger all caused by feeding just dry food (he still loves his biscuits now but it is a small amount that he gets). My cats love their raw food, I usually sprinkle a handful of biscuits on top between 4 cats so they don't get a lot each.

I know male cats are more prone to it than female cats as their uretha (think thats the one, lol, the tube from bladder to ouside) is different to female cats and crystals can form causing them to get reccuring cystitus. I also know that female cats can suffer with it as well. If you are feeding totally on dried food make sure that it is a meat based food as cats are carnivores and also keep plenty of water available and an eye on her output of urine.

Having said all that, lots of cats are fed on dried food totally and have no problems what so ever, maybe I was just one of the unlucky ones.