Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your girl has symptoms of increased panting, refusing to eat, and has vomited several times.
Panting can be a sign of pain, anxiety, nausea, low oxygen levels due to heart disease, anemia or lung disease or changes in blood gases due to organ disease. If her gum and tongue color are nice and pink then primary heart or lung disease or anemia are unlikely. I suspect then that her panting and inability to settle are due to gastrointestinal upset/nausea because she is refusing to eat and has vomited.
In most cases vomiting is triggered by eating something they should not, too much table food, too many treats or something they find outdoors.
While a viral infection is possible, they are less common in dogs her age.
More serious causes of vomiting include chronic pancreatitis, esophageal reflux, a dietary allergy or sensitivity, inflammatory bowel disease, internal organ failure (kidney or liver disease), a full or partial gastrointestinal obstruction or even infiltrative cancers such as lymphoma.
Because this has been going on for several hours and she is an older pup ideally I would recommend she see her veterinarian.
If you absolutely have no way to get her to a veterinarian and she feels well otherwise (no fever, no abdominal pain, bright and alert) there are a few things we can try to settle her stomach at home.
To try and settle her stomach you can give either:
1) Pepcid ac (famotidine) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at a dose of one half of a 20mg tablet per 20 to 40 pounds of body weight every 24 hours
These are acid reducers and should help her feel better. They are quite safe and can be used for a few days if necessary.
I would pick up all food for 24 hours from the last episode of vomiting and water for a couple hours to allow her stomach to settle after the acid reducers. When you give her water in a few hours make sure it is in small amounts only. If she drinks too much too quickly that can lead to vomiting.
After her 24 hour food fast offer a bland diet of 1/3 boiled, minced white skinless chicken or boiled, lean hamburger and 2/3 boiled, plain, white rice mixed with some low salt chicken or beef broth to make it easy to lap up and swallow and get additional fluids in.
If things go well feed her the bland diet for 2 to 3 days then slowly start to mix back in her regular food, a little more at each meal. It should take about 5 to 7 days to slowly convert her back to her regular diet.
If she continues to vomit, runs a fever (more than 103F rectally), has a tense painful belly or if she refuses to eat she should see a veterinarian for an examination, diagnostics, injectable anti-nausea drugs intravenous fluids and supportive care.
Please let me know if you have any further questions.