What is the healthiest wet cat food?



My 10 year old Siamese girl has been sick and has lost a lot of weight. Her appetite is there but she only eats a few bites of food. She loves wet food but is finicky - her favorite is 9 Lives Super Supper, but since shes eating so little Id like to get something a little more nutritious into her, maybe even a prescription food? SO whats the healthiest most nutrient dense WET cat food?