Could be pancreatitis, could be a lot of things. It's a big problem to not be eating for any length of time, especially for a diabetic cat. The best thing would be to take her to an ER vet if there is one near you, failing that use whatever tricks you can think of to entice her to eat. Try adding something extra-yummy to the food-- tuna juice, a sprinkle of parmesan cheese. If she seems nauseated (trying to eat, then turning away), try elevating the food and water bowls a few inches.
Are you home-testing? What insulin are you using? Skipping shots in a cat that isn't eating can lead to the development of ketones, which can develop into DKA, a life-threatening condition.
At the very least, if you are not already, you must test for ketones-- you can pick up the urine test strips at any pharmacy with other diabetic supplies. To catch a bit of urine for the test (you only need a couple drops), some people are able to use a long-handled large spoon, others have had good luck with putting a bit of crumpled plastic wrap in the box where the cat usually pees.