Hello and thank you for your question on Petco Pet Education Center, formerly Petcoach!
It is hard to say exactly what is causing Sash's symptoms without examine her, but I can offer some possibilities.
Coughing can be a sign of an upper respiratory infection, lung disease, lung cancer, heart disease, or feline asthma. The only was to definitively know what is causing Sasha to cough is for a veterinarian to do an exam and perform an x-ray of Sash'a chest so her heart and lungs can be visualized and evaluated.
Whether it is too late or something that can be cured depends on what the diagnosis may be.
I hope this has helped and I wish you and Sasha the best of luck!