Sudden food changes may cause GI upsets. Since she is accustomed to dry and you have to get her to eat, you might try gradually mixing in Evo Cat and Kitten dry, replacing about 20-25% of the food each day, until completely switched. If is 1 on the only low carb dry foods out there. The other one is Young Again 0 Carb (internet orders only) and is pricey, though they supposedly eat less on it. Once you get her switched to the Evo, you can gradually switch to low carb, over the counter canned. If you are already giving insulin, you need to be home testing the blood glucose with an inexpensive human glucometer to monitor for safety. A diet change may reduce the blood glucose 100_180 mg/dL and drop the insulin by 2 units.
Next, what insulin are you using and what dose? Humulin/Novolin and Vetsulin/Caninsulin generally do not last long enough in the cat to go 12 hours between shots. BCP PZI, ProZinc, Lantus, and Levemir generally do last long enough to shoot ever 12 hours a.d possibly get to a diet controlled state.