Hi there. Thanks for the question. Let me see if I can help.
Most likely this is a sign of oral (mouth) pain. She likely has dental issues or a bad tooth. At her age, this is something that happens often.
Other, less likely possibilities, include an oral tumor, some (like a sewing needle) stuck in her gums or between her teeth), or focal seizures (least likely).
I would recommend having her in to see a vet for a dental evaluation and cleaning if necessary.
In the meantime, if you dont already, feed her moistened or softened food, to make it easier for her to eat.
I hope this has been helpful. Best wishs