Good Morning and welcome. I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
My concern for Nancy is that she either is suffering form Kidney Failure which shows as vomiting and lethargy or that she has pneumonia or cancer in her lungs. Because of the possibilities for Nancy's issues, it is important that further diagnostics be done to find the problem. This will best be done by a veterinary specialist. Your vet can refer you to one that can perform these diagnostics.
I wish I could tell you what is causing this but, without more information from the diagnostic tools, we will not know how best to help Nancy.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please Reply so I can clarify for you
Sincerely, Dr. Loretta