First, I would advise you to NEVER give the injection without the dog having eaten. The dangers of the insulin making the dog hypoglycemic are far danger than the hyperglycemia that would result from missing an injection.
I would try mixing a little bit of wet canned food into her dry, so that each piece of dry kibble is coated with the moist food. If she eats this, then give her the insulin injection. If she doesn't eat, pick up the food and skip the injection. She may have high blood sugar for a short time, but not long enough to cause harm.
I hope this information is helpful.
Good luck with her.