I hate to give you an almost empty response, but I'm not sure. I would call the vet and ask what they thought. I know you said she has appt to be spayed and teeth cleaned this month. Maybe she's in pain and afraid of you touching her mouth as it would cause further discomfort. IDK? The teeth chattering has me baffled as I have never seen or heard of that, but who knows?!
I know when I had a toothache, it hurt to touch my cheek where the bad tooth was....Not saying at all that's what this is, just a thought.
