Hi Emma, waving from Surrey!
My first diabetic, Bertie, was also diagnosed at age 8, and he lived to be 20, bless him. With good care and just a little luck a diabetic kitty can live as long and as happily as a non-diabetic.
As said further up the thread, just feeding twice a day is very 'old school' thinking. And in fact the RVC's guidelines say that if a cat is used to being free-fed or is a grazer then they can continue to do that.
However we just advise that the cat does have a good meal on board prior to being given a Caninsulin injection. So, you do need that the kitty is hungry enough to eat a decent meal at that point. And it is helpful to wait 20 - 30 minutes after feeding before giving the injection, just so that the food has a chance to get into the system before the insulin takes effect. If the kitty needs to be distracted during the injection then it's fine to give a wee snack or a couple of treats.
Once the blood glucose gets under better control the appetite should become more normal. So please don't worry.
Also, as said above there is another insulin in the UK that's licensed for cats now, called Prozinc. But many vets are still prescribing the older Caninsulin. This is often because Caninsulin is just what vets have been used to using for a long time. And Caninsulin is also cheaper than Prozinc so may be prescribed where cost is an important factor. However, although Prozinc has a higher upfront cost it also usually has a longer shelf life once opened, and this can help to balance out the cost somewhat.
If you find that your kitty isn't doing well on Caninsulin then it should be an easy matter for your vet to switch to Prozinc.
It is good that your vet has started on a sensible low dose of 0.5 of a unit.
It's great that you want to hometest blood glucose. Good for you! This makes managing feline diabetes safer and more effective. And many UK folks use the Gluco Navii meter.
Regarding diet, what was Mitzi eating at the time of her diagnosis? And can you confirm what she is eating now?
Eliz