It could be a tumor in her intestine. I had a cat who vomited every day, sometimes projectile vomiting, for 2 years until he had lost half his body weight. He was always hungry, would not eat the dry cat food, and I was cooking for him for most of that time. The animal had EVERY expensive test that the vet suggested. I even questioned the vet about cancer and the answer was always, NO, the tests came out fine. However, after the cat was put down, I found out that one test was never done.