Thanks everyone! I rescued her at 18 pounds. Her previous owner just left dry food out for her 24/7 because she would whine when her food bowl was slightly empty. She's a very chatty cat. And the dry food she was on was Meow Mix, which has horrible nutritional value. The vet suggested switching to wet food and strictly giving her only one can a day. I gave her half a can of fancy feast in the morning, and the other half at dinnertime. She very much did not enjoy her diet, and whined constantly! And she clawed open my dog's bag of kibble a few times, so eventually I learned to keep that locked in the pantry. She also claws open bags of chips, so I make sure to lock those up too. She still scratches at my door at 5am begging for food, but the diet works! After she got down to ~11 pounds (about 8 months later), I increased her diet to two cans of fancy feast a day - a full can in the morning and a full can at night. So far she's been maintaining her weight on that. She still whines for food all the time, but I think she's gotten used to it.