There are a multitude of reasons why you cannot have this discussion -- all or any or which can be going on inside your therapist's head. You do not get to decide for her what she thinks or what she wants or with whom she chooses to have a discussion in her free time. I think Stopdog's signature line really applies here: Selfishness is not living as one wishes to live, it is asking others to live as one wishes to live. Just because you want someone to behave a certain way in interactions with you does not give you the right to force the other person to do so.

You obviously can choose not to continue a therapeutic relationship with someone who chooses not to chat with you in public, but let's don't try to pretend like it's the other person who is imposing on you by holding to her own boundaries.