If her blood sugar is falling so drastically, I would honestly want to get her started on some nutrical paste. It is a high calorie paste that you can get from your vet. It will help to perk her up and might even stimulate the appetite.
Try to let her go no more than 2-3 hours without eating something. Jarred baby food meat works well and most dogs like it.
If she's been this long without food, she may also need sub-q fluids.
You have to keep in mind that this age is geriatric for this breed and that many health risks become worse for these older dogs.
Go ahead and see your vet today for further help.
Let me know if you have more questions.
