[Her shoulders grow more and more tense with his every word.]
Don't you think I've tried? That if I knew how, I would do it? [No, of course he doesn't think so - everyone must think this is all on purpose on her part. When she finally turns to face him she probably looks more aggravated than she really is, although having seen the movie he might realise it's all frustration, not anger.]
You can enlighten me on how exactly I'm meant to stop it, or you can turn and leave. [With "turn and leave" being his only option in her mind.]