Bulldogs World

We adopted a 6 year old girl in October last year.  This is her first summer with us.  We have another bulldog and are familiar with the breed. Last Monday (10 days ago) she started wheezing- worse than typical heavy breathing panting.  She sounded very restricted.  Took her to ER vet. Chest x ray good, lungs clear, "irritated trachea".  They gave her a steroid shot and sedatives to take home.  She seemed to improve over the next three days, but then on Friday she was much worse. Got her in with regular vet who gave prednisone, and some sedatives, said her lungs still sounded clear.  She proceeded to get worse.  Took her to a different ER vet on Tuesday evening (8 days after initial onset). She sounds like she needs to cough but isn't, and the wheezing is much worse.  They AGAIN said her lungs were clear, normal bloodwork, and suggested exploratory surgery for her upper airway.  We do not know the cause, or if this is something she goes through every summer in the hottest part (as we have not had her during that time before).  She is laboring to breathe, using a ton of abdominal effort. She is still on sedatives from the doctor. 

Any advice or experience?  We just want to get her through this episode and get her airway back to it's normal openness!