She stopped eating her dog food (Blue Buffalo) and lost interest in licking plates when I finished eating something she enjoyed that I made.

This is a common sign of an old dog's body shutting down, I'm sorry. Feel free to take her to the vet, and be prepared for a speech about all the tests you can have done - or not.

Many of us have paid for all those tests, and some have even paid even more for treatments, and only you can decide when it's time to let go. I'm sure your vet will say 'Let her eat whatever she wants.' Maybe try cooked eggs, hamburger, rice (all soft in case her teeth hurt or her whole jaw). But if she won't lick the plates, she may not want any of it. Is she drinking water? Excreting OK? Showing any signs of pain?