Welcome to YorkieTalk
I agree with Wylie's Mom. Little Bruiser needs to go to the vet for a good ole fashioned checkup including bloodwork. It sounds like there may be some underlying issues that might be causing the loss of appetite. I am glad to hear that you are going to make an appointment when this holiday weekend is over.
Please be sure that Bruiser takes in enough calories to sustain her until you can figure out what is going on. You don't want hypoglocemia to add to her discomfort. If she won't eat her regular food, offer something special - maybe some homemade chicken/rice with a few veges tossed in for good measure. You can also rub her gums with a bit of Kayro syrup, but if you go this route, be absolutely certain that she eats a slow buring carb - if not she can have an energy spike followed by a crash.
Good luck!