I wanted to get the first response in immediately before giving a more detailed response. In a cat the age of 6 there are a few conditions that can cause this. If she hasn't been eating for a while now she may have a foreign object lodged in her intestines that has perforated, a liver condition as a result of not eating called hepatic lipidosis, an underlying heart condition called hypertrophic cardiomyopathy that results in a weakening of the heart muscle. As the heart enlarges or stretching clots can break off and become lodged in any area of the body including the brain, spine, and even the lungs causing the labored breathing you are describing. There is also a possibility your cat has gotten into something toxic, moreso if she goes outside, but there are inside dangers aswell. Common toxic ingestion includes, certain plants, antifreeze, and rat poison. Again if she is outdoors she may have been hit by a car, or attacked by another animal and is suffering from internal injury. Many cats also have asthma which is inflammation of the bronchial tubes or lower airway. This condition can become severe and life threatening aswell without treatment. No matter what scenario may be occurring right now your girl is in serious danger and needs immediate treatment if there is to be any chance of recovery. Please let me know if you need more information.

Thank you

Theresa