I don't think it is unreasonable to expect a reply from her to stay connected but I believe it would depend on the T. I don't think Ts would not necessarily do that but would wait for session time itself.

Maybe it is something you could agree with her, going forward i.e. in case she gets sick for a long duration maybe text/email/phone call could be set up for her to check-in with you and stay connected? I think it's the least she could do but... Ts comes in different stripes.

I'm sorry your T had to cancel on you (or postpone her coming back). Again..