Has she been tested for IBD or Pancreatitis? I think these are not detected by just bloodwork, but other test may be necessary. An unregulated diabetic cat can need more food than a non diabetic cat, and I think she needs to be eating more than a couple of teaspoons of food 3 times a day. My cat eats 3 cans of fancy feast a day, spread out between amps +2, +3 and +5. I know there is a formula for how much food per weight a diabetic cat should eat. I think it is one ounce of food per one pound of the cats ideal weight. So if her ideal weight is 11 pounds, then she should be eating 9-11 ounces. Every cat is different however, but Im pretty sure this is the formula. The reason a diabetic cat always acts like they are starving, is because they are. Their bodies arent able to use the food that they eat properly, which is in turn why they lose weight. If she were mine I would be taking her to another vet who is willing to do the testing that she needs to figure out why she is vomiting so often. As I have said before, Im not an expert..I do have 3 cats and my sugar cat Chi Chi has been on insulin for almost 7 months now. I hope you get to the bottom of her vomiting issue soon, poor kitty must be miserable.