I don't read her as being sarcastic in her tone, more businesslike and a bit detached. I agree that she should have wished you well in your surgery. But she is offering to see you, so she is trying to accommodate you. I think with her comment about the meetings, she's trying to let you know that her reason for canceling is not about you, but about the meetings.

I say this as someone who has a tendency to read negative things into tone in emails/texts, particularly from therapists, so I get it. But I know it can often help to have an outside opinion of it.

Also, because she said she normally knows about cancellations at the beginning of the week, I'd suggest checking in with her to be sure you can get a session before your surgery.