Move on. I think that you and she should agree that if you're in the middle of something, she can say no to what she can't do, you're going to accept that, and she's going to keep quiet about it. Move on to something else, move on to lots of other things, have fun. Later, if she still wants to discuss her feelings, then you can re-assure her, etc. But it might be easier to do that after she's pleased you in lots of other ways, rather than right when she feels that she's disappointed you. And I, personally, don't like that dynamic of stopping the action to discuss whether she's a bad sub. Obviously, it's different if someone's in crisis, but otherwise, I would just postpone that conversation.