Welcome!
Unfortunately, frustosamine tests cannot give accurate enough data to base dosing decisions on--they give an average of blood glucose levels over a several week period, and do not tell you how the insulin is actually working in your cat.
Normally, we say a cat is in remission when he can maintain a daily blood glucose level in a normal range (50-120 on a human glucometer) for a period of two weeks. Often, cats do best when they are weaned of the insulin with gradual dose reductions--when Bandit went into remission, he went from 1 unit, down to .75u, to .5u, to .25u, to .1u over a period of many weeks.
Are you testing your cat's blood glucose levels at home? If so, this would be the best way to know if your cat still needs insulin and how it is working to lower his blood glucose levels. If not, there are some
wonderful resources here that can teach you how. It's something that seems scary to some people at first, but even fractious cats will accept it after a little while if you use lots of treats.

If your vet isn't very experienced with feline diabetes, she may not know that the current treatment recommendations advocate home testing over office curves and fructosamine tests. It's the only way to accurately know how your cat is doing. Hometesting will tell you if your cat still needs insulin, or if the dose should be raised or lowered. If you have any difficulties, or need any advice on how to hometest, there's a whole forum full of people here who can help you out.
I would strongly recommend
not to remove the insulin before you know how the dose is working for your cat. Suddenly removing insulin from a cat who needs it can cause a deadly complication of diabetes called diabetic ketoacidosis (DKA).