Would you consider that you have grown dependent on her? Have you thought about your own responsibilities and expectations concerning your own participation? This might be something else to sit down and discuss. Is it fair to her that you not say anything? How is she supposed to treat you if this is the case?

Things I agree you have reasonable expectations for: communication and provisions for while she is gone.
Things I'm not so quick to agree with: I think we have our own responsibility to participate in a session - fully. We need to do our part and can't expect therapy to be successful if we don't. It is possible the lack of communication is two sided. I think we owe it to ourselves to be proactive... ask for provisions or a plan of action for emergencies while she is away - and not by email.