My name is***** and I will be able to answer your question tonight. I have very good news for you-
The cocoa powder used for hot chocolate is usually very weak (Swiss Miss, Starbucks, etc), which means that it is minimally toxic. If your dog ate the entire box, this could cause problems, but a small portion of one packet is of no risk.
If you were drinking the fancy homemade Mexican hot chocolate, this is much more potent, and I would not allow your dog to have access to it. But if she only licked a residue off of a cup, even with the stronger product, she likely would have not ingested nearly enough to be toxic.
Things to watch for tonight-
vomiting or diarrhea
If you don't see any of these signs, she did not receive enough chocolate to have toxicity and you can rest easy tonight.
Does this help? Do you have any more questions?