I found a few examples at ALC, but still not sure about the best way to say it.
For example, the most natural way of translating this expression
can be rephrased simply as follows:
Basically it is a fancier way of saying ～ことをまったく知らなかった where ～ is the statement that follows the expression.
I find the most natural way of translating this is to write 彼女は（息子が怒り出す）とは思わなかった, to show that the person was kind of caught off guard by what happened.