Did your t know why you cancelled? Maybe if you explain that you were unexpectedly ill she may cut you some slack. I think it is reasonable to discuss your concern with her.

My t has a 24 hr cancellation policy but if I were genuinely ill and let him know as reasonably soon as I could I don’t think he would charge me. Like you, I show up, rarely cancel and pay on time. Some clients may cancel as a way of acting out but you are not that client.