I'm very sensitive to cigarette smoke so I know how you feel, but she may have no idea at all that it's a problem for you. How about assuming that she doesn't know, telling her gently that it's a problem, and asking if there's any way she could smoke further away from the building?

My dh's aunt and uncle smoke like chimneys (even though he has had multiple health problems including heart disease greatly aggravated by smoking and SHE WOULDN'T EVEN QUIT WHEN HE TRIED TO) but they have no idea that they reek of smoke at all times. I stayed at their house once and we slept in a so-called "smoke-free" guest room. I had trouble breathing and came home with a sore throat that lasted a week.