Have you tried giving her broncodilators by mouth?
As you are probably aware prednisone has lots of side effects. Before making that permanant decision I would recommend that you take her to her veterinarian for tests.
Since there are so many causes of vomiting I think that testing her to see if the cause is something treatable or curable would ease your mind. You can always make that final decision later.
There are many common causes of vomiting that are controllable such as: IBD, Hyperthyroid Disease, Diabetes, food allergies, gastric ulcers, and others. She should also be on a hypoallergenic, high protein, grain-free diet for the excess weight.
My answer is of course only for advice, only you can make that ultimate decision, but being prepared with medical answers, may make it a bit easier.
Sincerely, Dr. Cheng