Yes, you can get sugar-free/diabetic candies that are not hard candies. You don't say how old your granddaughter is, but I would tend to focus on giving her non-food items, such as stickers, crayons, coloring books, dress-up jewelry, etc.

Diney - I was just getting ready to say that warning myself.  I found out the hard way!!   

When my son (not ADHD, but overweight) wanted candy, I used to give him sugarless bubblegum.  He liked that even better than candy. 

Our school has a no sugar treat policy for when the kids bring treats to school to share (sugar cannot be listed as one of the first 2 ingrediants and homemade treats aren't accepted).  So, the kids end up trading small toys and trinkets or bags of pretzels, sugar free bubble gum (as was already suggested) etc.   It is a little frustrating b/c it is way easier to buy cupcakes and cookies for treats, but you can find things. We can bring in ice cream treats--I haven't really figured out how that passes the "healthy" test, but it does, so I will not argue.  Most parents send in apples, grapes, cheese sticks, pretzels and crackers.  No pnut better b/c we have a few kids in our school w/severe allergy and they aren't allowed to tell anyone who it is, so no one can bring in pnut butter.