I am so sorry to hear that Baby seems distressed, panting, refusing to eat or drink, and won't settle and lay down.
Panting and pacing can indicate pain, but it can also indicate low oxygen levels to the brain.
In an older dog we do need to worry about arthritis causing her pain, but that is unlikely to create such a sudden change in her with no previous history of limping, stiffness or pain. Most dogs that become that painful from arthritic pain show some symptoms before things get that bad.
Organ failure could cause metabolic waste build up and changes in blood gases which would lead to panting, and a loss in appetite, but these changes are generally more gradual.
A normal dog has a resting respiratory rate of about 10 to 15 breaths per minute, and one breath is considered the in and out motion of her chest. If she has a rate faster then 40 breaths per minute consistently then she is in trouble. If she doesn't have a nasal discharge and isn't sneezing then her panting is likely related to a problem in her chest or secondary to anemia (decreased numbers of red blood cells).
Problems in her chest leading to an increased respiratory include primary heart disease (including cardiomyopathy, heart valave disease and secondary heart failure, and heartworm), primary lung disease, bacterial, viral, parasitic (lungworm) or fungal infections, a mass(es) in the chest including lymphoma, heart based tumors or carcinomas, or fluid around the lungs (pleural effusion) due to a mass, bleeding, chylothorax or an infection.
Unfortunately because she is older cancer or heart disease are big concerns. An abdominal tumor could place pressure on the stomach and intestines causing her to feel full, and thus not want to eat. Or she may be struggling so much to exchange oxygen she has lost her appetite.
I recommend rechecking her gum and tongue color. If they are not a nice bubblegum pink color then we do need to worry about internal bleeding or heart disease or primary anemia. If her color is pale that warrants an immediate veterinary visit and if your veterinarian is closed now then take her to an emergency clinic. I don't mean to alarm you too much but if her gums are pale this is a true emergency.
If her gum color is fine and you can try an acid reducer to see if that settles her stomach and gets her comfortable enough to eat at least today, then I recommend she see her regular veterinarian tomorrow for an examination and some diagnostic testing. Keep her very quiet today.
Acid reducer to try include either:
1) Pepcid ac (famotidine) at a dose of ¼ of a 10mg tablet per 5 to 10 pounds of body weight every 12 hours
2) Prilosec (omeprazole) at a dose of ¼ of a 20mg tablet per 10 to 20 pounds of body weight every 24 hours
These are acid reducers and should help him feel less nauseous. They are quite safe and can be used for several days if needed.
To decrease the symptoms of stomach upset and coax her to eat you can offer her a bland diet for the next couple of days. A homemade bland diet is a mix of 1/3 boiled minced white skinless chicken or lean boiled hamburger and 2/3 boiled white rice mixed with some low salt chicken broth to make it easy to lap up and swallow. Feed small meals frequently.
Please let me know if you have any further questions.