I am sorry to hear you are worried about Emma. My name is Rebecca; I am a veterinarian and will do my best to help.
Some additional information would be helpful. Have any blood tests been done? Was a stool sample checked microscopically for parasites? There are parasites that are not worms, and Panacur might not help with those.
Panacur would not normally cause diarrhea.
Dogs will not starve themselves. If a dog is not eating normally, that tells me there is something wrong: liver disease, pancreatitis, kidney disease, infection, and the list could go on.
It will help to know if any blood tests besides the test for Lyme disease was done. A positive Lyme test indicates exposure to Lyme disease, but not necessarily infection. Many dogs (and people) are exposed to Lyme, make antibodies, never get infected or sick, but will test positive on a test.
Let me know what else I can answer.