That's awfully late to cancel. I would let her know how it affected you if you can next session. If you say, "no, that's fine" then she may not know to what extent it bothers you. My T would tell me when she was going away several months in advance so we could work on that and give me a little more detail of her situation if she had to cancel or was going to be late, etc. so I could at least understand. My day was Friday too but then she started going to classes on Fridays and had to swap days so much we finally decided to change to another, better day for her even though I'm pretty bad with changes.