I've found that canned cat food helps, as well as tuna, salmon, etc. You can give a little bit of puppy food here and there, a well as cooked pasta, raw liver(chicken or beef, no preference), you "can" cook the livers, but the smell is gawdawful(or is that just me?). Yogurt is good, soymilk/almond milk via water bottle is well-enjoyed and gives some calories. You can also go to your veterinarian and ask for a few cans of Hills Prescription Diet a/d. It has calories and fat galore and is meant for putting on weight or animals recovering. Each can should only be around $1 or so. You can give a bit of that every day, and it will help her keep the weight on better.