Unlike exposure to other toxins, many Agent Orange symptoms tend to take several years to decades to present, and can cause a host of health issues. Initial symptoms tend to include common side effects found with many other illnesses, as well as neurological and psychological problems.
Heavy breathing or panting. Most dogs will pant from time to time because they are stressed or excited, but when dogs pant for no apparent reason and the panting becomes excessive, this can definitely be a sign that a dog is experiencing pain.
Things such how old she is, what kind of dog she is, if she's been running or playing would be of great help. Panting can obviously mean that the dog is hot, but my dog started panting a lot when she got arthritis and she was in pain. I would definitely get it checked out just in case.