The issue we are having now is she appears to be having dry mouth most nights and is constantly smacking and swallowing.
Highly doubtful that what you are describing is a dry mouth. If your dog had a dry mouth she would go get a drink. Those are symptoms of nausea. Long shot but it could also be a bad tooth.
How long after she eats does this happen?
She might be cancer-free however due to having a MCT in the past her body naturally makes TOO MUCH histamine. Too much in the tummy can cause nausea.
Thyroid issues can also cause nausea.
I'd ask the vet about doing a trial run of Pepcid for a while to see if you notice a difference. Wouldn't hurt AND it might solve the problem.