Upstairs Neighbor is Smoking, what can I do?

I live in a rowhome and although the walls are not necessarily thin, when the neighbor upstairs smokes the stench is unbearable! I talked to her this afternoon and she even though she admitted that she smoked, she tried to convince me that the smoke was coming from "somewhere else"! She even tried to convince me that it was coming from the apartment next door, but when I told her it was vacant she had a blank look on her face. I can smell the smoke again and she said she "Only smokes three cigarettes a day" She told me she also has cancer now and she says she even smoked while wearing the patch. I really don't know what else to do. I've complained to the landlord before but I wasn't sure who it was coming from. I don't want to seem like a pest about it but would be it rude to keep a week-long log of when I smell smoke and write the neighbor a letter via certified mail telling her this is when I have smelled smoke from her apartment? I am trying to really let her know that it's annoying. She seemed like she was more interested in making me think that it wasn't a big deal but I was very polite but direct with her today when I told her the smoke is bothering me. Now what?