Sores on roof of mouth
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It's doubtful that kibble would cause this. Something she was chewing... maybe. Personally, I would keep an eye on it over the next couple days/week and note through photos whether the condition is improving or not. The photos will give you something to actually show the Vet (much easier than explaining it). Meanwhile, observe your dog's eating patterns, energy level, and chewing habits for obvious changes and indications of injury/illness.
If you do go to the Vet, please update us all on the results. :)