I had a cat with diabetes. It was tough to deal with, we gave him shots twice a day, if I remember.
Our little friend Hildiekatt Halfshadow the Harrier (Hildie for short, aka Monkey Baby) has diabetes.
I give her a shot twice a day. I've gotten her to associate it with getting a few "Greenies" stomach treats and a little bit of milk (no more than a tablespoon at a time). She is not lactose intolerant, and really likes 1% milk.
I put down a couple of treats, which she eats, then I put down the little bowl and a couple more treats. I pet her a little and she lays flat when I pinch up the skin between her shoulder blades. After I administer the insulin, I pet her again, telling her what a good girl she is and then say "All done!" She then eats her other treats and laps up her milk.
If I'm a laggard in getting her the treat, milk and shot after her breakfast or supper, she comes and paws at my leg to remind me.
We'll be going to see Doc Knilans (our vet) on Friday morning to see how the insulin is doing for her. Her initial blood sugar readings were in the mid 460's. Last check they were down to the mid 250's.
Keep at it for kitty, the diabetes is controllable. Ive's also been weening the girls off of dry foods with grain in them, plus feeding only minced or pate style canned food. The gravy ones are higher in carbs. And, some of the big brands (like the Friskes I feed the 3) are actually lower in carbs than the premium brands.
Opus88 has posted some excellent links about kitties and diabetes.
Cushing's, I know that can take a bit of work to get the meds right. My brother in law has that. After they found the right balance, he's been doing fine. Your kitty will, too.