She's right though. Good relationships can fluctuate for reasons that have nothing to do with the relationship itself. No one can be 100% consistent in how they act; that would really not be human. So what you need to figure out is why you feel fear (use a different word if you don't like that one, but my gut is it is fear) when your T seems different somehow. What are you afraid of? And are those fears really about her, or is that old stuff coming up?