It's fine, Yang. Don't fret too much about detail! The biggest thing was that I didn't want you to read your whole letter, get to the end, and have her say something like, "Which appointment that needed to be cancelled?" or something like that that would come off as insensitive and would probably be hurtful, even if it was just because she didn't know which appointment you were talking about or why the cancellation made you feel lied to.

Good luck!!