Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your pup Poppy ate 500mgs of paracetamol (acetaminophen).
We see toxicity symptoms in dogs at a dose of acetaminophen higher then 75 mg per kilogram of body weight. At 8 to 10 kilograms she would need to eat 600mgs to 750mgs of acetaminophen. (8kg X 75mg/kg = 600mg, 10kilograms X 75mg/kg = 750mgs). So she did not eat a toxic dose if she only ate 500mgs. You should not see any symptoms of toxicity in her.
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.
I would encourage her to drink plenty of water tonight and watch her closely, but at the dose she ate she should be fine.
Please let me know if you have any further questions.