As a diabetic who controls the disease solely through diet (having at one time been on four medications for the illness) I can tell you that Splenda, is a better choice for controlling blood glucose than sugar.
However, sugar is not the worst culprit. White bread, white pasta, those sorts of things are worse than a teaspoon of sugar. Granted, many desserts require more than a teaspoon of sugar.
Remember that splenda/sucralose is sweeter tasting than sugar, so use less. It does not caramelize so you can't use it for that type of dessert.
As a diabetic my chosen dessert, when I want to use calories and carbs in that manner, is usually a small selection of cheese.
It's kind of you to want to make a special dessert for your friend who is diabetic. All too often folks with diabetes are not included in those sorts of things. It's really nice when someone cares enough to make the effort.
There are loads of recipes on the internet for nice desserts for diabetics. Remember that any recipe you have may be able to be adapted. Whole wheat flour (often if you use whole wheat pastry flour you'll end up with a finer texture) can replace all or most of white flour in cookies and other preparations. And as we've already said, sucralose can replace sugar.
I'd try to stay away from aspartame and saccharine, but that's just me.
Hope that helps a bit!
