You should take Lis to your vet as soon as possible. There are several possible causes for these symptoms: heart problems, lung disease, mediastinal tumor (common in senior dogs), etc. All these conditions can lead to pulmonary edema (the presence of fluid in the lungs), which generates breathing difficulties (gasping) and noise (wheezing).
On the other hand, if your dog was recently in a kennel with more dogs and the symptoms started soon after, it could be the kennel cough.
The best would be to take your dog to your vet, who will assess her and perform a blood test and chest X-ray in order to determine the cause of mentioned symptoms.
All the best,