Hi there,
Ordinarily, my first thought would be XCHT as well, but the pulse and tongue don't quite fit. Given the symptoms, tongue, pulse and time of worsening, I'd say you're dealing with a Jue Yin excess, and would suggest changing XCHT for Wu Mei Wan, unless the dog is notably improved on XCHT. The two can be used together if you're not sure.
Jue Yin excess is tantamount to an upbearing pressure from the lower abdomen due to Yin deficiency, causing Stomach Heat. It's the main cause of GERDs in the middle of the night in people, and I suspect you're dealing with it here in a dog.
Let us know how it goes!
Steve