<<I've had a diabetic student at the dojo once.
It is quite likely that you've had several diabetic folks at the dojo
but one of the two of you were probably unaware of that fact...
or perhaps both of you were unaware. It is not a scare tactic, but in what is known as Type 2 diabetes, (aka Adult Onset Diabetes) most have no idea they possess the illness-condition, until they are actually diagnosed. It can be that subtle, unless somone knows what to look for... it is a bone-fide Epidemic and shows no signs of decreasing.
Now back to your post, in the event of LOW blood sugar (regardless of the type of diabetes) a candy bar would not be the ideal "cure", or frankly even a slightly good one from the standpoint it will take a longer time to breakdown the nutrients, and when you add in the Chocolate, the fats... (ie getting access to the sugars in the candybar...) it is a very poor choice... of the many available anyway.
Consider instead something you can get at any pharmacy, and many grocery stores these days called GLUCOSE Gel which comes in a small tube. It is a brand name product which has many generic variations these days all of which defacto are essentially a small tubes of cake icing +/-. (ie which btw is also a viable alternative in place of the brand name Glutose product, simply some tubes of the normal cake icing that you get at the grocery store)
In terms of an emergency, or even a small incident, it requires nothing except removing the cap and squeezing the tubes contents into the diabetics mouth... (typically in 2 or 3 squeezes to prevent spillage/gagging... if you squeezed the entire thing in...)
As a cure for a low bloodsugar incident, it's a little over the top most times but if/when woozy or unable to communicate clearly it does the trick, fast and easy... 15-30 minutes.
Ask your student what they want you to do if/when they are "low" (aka Hypoglycemic, aka HYPO, shocky, etc., etc.). But the small tubes of cake icing, or the Glutose Gel are an easy addition to the First Aid Kit and a heck of a lot easier than a can of NORMAL soda, Smarties Candies, whatever the typical solution-cure for a "low" sugar might be. It fits into the first aid kit, cheap, lasts forever, just like on the grocery store shelves). Easily eaten even by combative diabetics... (there's a pun there someplace)
Its merely my opinion, and I could SURELY be mistaken,