Ours had gotten that same thing. We think it was a bee sting or something. Could be a reaction from a plant too..?
If you're worried about your pup you need to call the office. It's very unlikely you're going to get a veterinarian on here to answer your questions. They're an extremely busy place.
She was probably stung by a bee, give her some benadryl and get her to the vet.
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