geez, my poor 15 pounder only gets half a 5.5oz can of food a day (1/4 twice a day). He's always hungry, but that's how he got to be 21 lbs in the first place.
My fatty got a UTI when I tried clay clumping litter - I guess the dust somehow plugged him up. He was about his fattest then so he couldn't groom himself all that well.
I actually mix up his wet food with a tablespoon or so of water and mush it up like a puree; he gets more fluids that way.
Hope she's starting to feel better!

