We see toxicity symptoms in dogs at a dose of acetaminophen higher then 75 mg per kilogram (2.2 pounds per kilogram) of body weight.
At 12 pounds he is 5.45 kilograms, so he would need to eat 409mgs of acetaminophen. (5.45kg X 75mg/kg = 409mg)
She ingested 500mgs (2 X 250mgs = 500mgs), so she ate a toxic amount.
Signs to watch for with acetaminophen toxicity would be brown or gray colored gums, difficulty breathing, edema or swelling of the face, neck, legs or feet, vomiting, yellow color to the skin and in very severe cases coma.
Aspirin can be given to dogs, but the dose is 5mg to 10mg per pound of body weight. For a 12 pound dog that is 60mgs to 120mgs. She ingested 500mgs, at least 4-8 times a normal dose. Possible symptoms of toxicity include vomiting and diarrhea, possibly bloody, gastric ulcers, possibly perforating (ulcerating all the way through the stomach wall) and secondary peritonitis and increased bleeding as well as possible organ failure.
When two nonsteroidal drugs are given at the same time the odds of side effects increase by several times the normal risk, they potentiate each other's side effects.
Caffeine can damage the heart, lungs, kidney and central nervous system. A lethal dose is considered to be around 70 mg per 1 lb body weight or 840mgs for a 12 pound dog. She ingested 130mgs, so not a lethal dose, but enough to cause an irregular, fast heart rate and rhythm and further stress her other organs.
She needs emergency care as she has eaten toxic levels of two drugs, and a dangerous amount of the third.