Shas; I figured I'd start a new thread on this.... you were asking about high protein / low carb foods. Not sure if you feed wet and / or dry food so here goes the bit that I can share. But I will double check with a friend of mine tomorrow who knows all the in's and out's of the different cat foods.
However off the top of my head some foods you can try are Hi-Life and Natures Menu - both available from Pets at Home. I've just checked a pouch of Hi-Life that I have at home and it's about 50% meat content. It has no grains but it does have tapioca as a binder (to make the jelly stuff). As a comparison, Foods such as Felix and Whiskas typically have about 4% meat content; and they both have added sugars which may also affect Candy's diabetes. Another really good and very cheap food to try is Butchers Classic tins - again, I just looked at a tin and it's 48% meat with no added cereals (not sure about sugar, but it's not listed). Available from any super market and less than £3.00 for 6 tins.
Onother one are Feline Fayre black pouches; they also have a high meat content but also have glucose added; again not sure how that would affect Candy. I've only ever seen them at ASDA and Morrisons.
Dry foods are slightly more difficult and I cannot think of one that doesn't have carbs, but I'll ask on my cat forum if you want me to?
Again depending on what you're feeding now, the one thing to make sure of is that the wet food you're feeding is labelled 'complete' which means it'll have all the right minerals and nutrients a cat needs. Quite a few high meat content wet foods are what they call complementary so not enough. And if you do think you'd be happier feeding her food you've cooked yourself so you can monitor better then you'd need to add something like this http://www.zooplus.co.uk/shop/cats/supp ... ins/155860 to the food to make sure Candy gets what she needs. One of the main things missing in complementary foods is taurine (which is found is muscle meat and bones I think) and a lack thereof can lead to blindness.
I hope this is of some help