He might be developing asthma. I am sorry you smoke.
Hi! Asthma is the first thing that comes to mind... I always kept my cats away from smoking guests for this reason ( they were long haired cats at the time , more asthma prone than short haired ones)!
I had one with asthma, she sneezed and whistled a lot and was on madication, theophylline daily, and the equivalent of Ventoline,in a spray form. However, since you CANNOT spray a cat in the face, there is a canadian device that allows you to spray from a distance ( like a long tube, so the cat doesn t hear the pscchiitt!!!)
I would also have her heart checked. Sometimes sneezing and problematic breathing are heart related.Especially in older cats. best of luck and... Try and smoke away from her, in either case!