Have not seen the movie, but just listened to the episode. Not sure if this is period-correct as they may not have understood bacteria well enough at the time the story was set, but tuberculosis (like a lot of diseases) has a window of contagion. TB has to be active to be contagious. I know modern medicine limits the contagious period to a few weeks, and that TB can relapse if not aggressively treated, but I think the infection can go into remission naturally as well. There are a lot of ways this could be bungled in a period piece, but it's not outright bonkers for her to say that she's not contagious.
