Dogs don't show pain like we do. Instinct tells them not to yell out as they will look weak and become prey instead of predator. I wouldn't totally wipe this out since she did have a limp and is on arthritis supplements. If she received an injection of prednisone, or other steroid, this too can increase panting as well as thirst. Yes as mentioned early chronic allergies can create lung inflammation and result in excessive panting and coughing this may have been what the vet was seeing in the xray. Theophylline can actually improve breathing but also create anxiety or agitation which may be seen with panting. If she isn't on an antihistamine then trying benedryl at a dose of 1mg/pound may benefit her and it won't hurt to try to see if it helps. Give it to her three times a day. If she becomes more anxious while on it (a possible side effect) then it just negates the reason for trying it and you may need to try a different antihistamine.
When asked what advice she would offer to other dog owners, Catherine suggests that owners never assume that their dog is allergic to just one thing. If the dog has allergies, they are usually allergic to several different elements. She also suggests that if dog owners decide to use Prednisone, they should go with the lowest dosage available and look into giving them milk thistle to prevent against liver damage. Owners should be open to trying new medications and therapies and never give up. It’s important to try everything they can to keep their pup as comfortable as possible.