Congratulations on your new Yorkie baby!! When we brought our Toto home [at 16 weeks] she wouldn't eat anything for several days. It scared us spitless!! I took her back to the vet three times that week and each time she was just fine! She just flatly refused to eat anything! Our vet told us to keep a little bottle of white Karo syrup with us at all times in case her sugar dropped suddenly and later had us use the vet formula NutriCal. I keep a tube of the NutriCal on hand to this day and it's been three years. Since your parents are traveling with her, perhaps they might try some baby food? Toto has always been a picky eater and we have given her the chicken baby food and also smashed up the little Gerber chicken sticks.
Good luck and please update us on your baby. Can't wait to hear how you like her!!