I understand (believe me, I sure do!) how annoying this is BUT she may not be sick. It could be anything - an elderly parent breaking a hip and needing care, a sudden house move, if she has kids something going on with them, anything. It's useless saying not to think about the possibility of her being ill and in hospital, but do remember there are other things that throw a spanner in the works that aren't necessarily terminal illness.

I think, in your shoes, I would probably send an email back asking if she was ok healthwise, to put your mind at rest. You don't have anything to lose by asking, and the best outcome is that you get a reassuring reply that she's alright and you will definitely get a chance to pick up dialogue with her in due course.