There is sulfite in all the usual sugars and in the dextrose in the sugar substitutes.
Bottled lemon juice is always very high, over 100 ppm, in added sulfite used as a preservative. Frozen plain lemon juice is clean.
I would not trust frozen lemonade, not so much for the sugar, but out of suspicion of the contents of the lemon juice used.
I would also avoid anything else with lemon flavoring - teas, mixers, powders ... Even fish prepared with lemon, often the lemon is from bottled, not fresh or frozen plain lemon juice. It's pretty hard to find frozen lime juice anymore too!