I just bring it right up, even though it's hard. I say when you did X (run over time with the client before me a few weeks in a row), I interpreted it as Y (being mad at me/that she's more important), and it made me feel Z (sad, that i'm unimportant, etc.). In that particular example, it led to a really good discussion where my T asked me to consider other possibilities. I came up with the possibility that the other girl needed some extra time or that maybe her session started later. T was able to provide me with several other opportunities, including just that she's bad at keeping track of time.

She never did tell me the specific reason why it happened, because it wasn't going to be helpful for me. Discussing my interpretation, though, was very helpful. It showed me how I interpret situations as something negative about myself when really it might have nothing ot do with me. I've started to notice that I do this a LOT!

I would encourage you to discuss it for the same reason, because it could be really helpful. If nothing else, she can clarify her intention or feeling of the message. I had the same situation with my dietitian a couple years ago- I thought she was mad at me and i'd done something wrong due to a short email response. It turns out I misinterpreted the entire tone of her message. She wasn't mad at all. Good luck!