I remember you said you almost always get angry during your sessions. If the t doesn't have very many options of things to talk about that don't get you angry, then she's probably kind of stuck having to go back to talk about something that you don't want to talk about that made you angry. In addition to telling her you don't want to talk about mindfulness, you could tell her something that is helpful to talk about. You would have to be willing to consider at least SOMETHING to be helpful.