I guess I don't see a direct link or why you think it must not be a coincidence? Unless it happened right after you told her? And isn't she sort of weird and nonconformist anyway with maybe some kind of health issue, i.e., not the most in the moment appointment-remembering type of person anyway?

Life happens and we all miss appointments, but what would aggravate me is that it happened twice, and if she didn't apologize afterwards. I assume she explained her absence?