Dextrose is corn-derived glucose same as corn syrup. HFCS is also corn derived with the addition of fruit derived glucose. Dextrose is what is very commonly present in chocolates. Avoiding corn syrup absolutely would include avoiding every chocolate on this person’s list. HFCS is what is common in candies like lollies. Corn allergy reactions to glucose derived from corn are “unlikely”. Ftr the only reason the word is “unlikely” and not “doesn’t happen” is because science would never give an absolute one way or the other. Corn starch allergy reactions are more common and still incredibly rare and unlikely.