Tell her to shut the fuck up. (Obviously not quite like that.)
At the end of the day, she cant TELL you what to do, be your own man.
Tell her you will listen to her REQUEST and make a compramise. Dont smoke everywhere in the house, just chose one room... e.g bedroom, living room etc.
Stop letting some bitch boss you around, I bet you dont tell her to do stuff in the same context, like stop going out with her friends or whatever... something that is apart of her, like smoking cannabis is to you. Its not fair to expect that of a person when you knew it about them in the begining.