Surely this woman has exercised her absolute right to leave this country. However, by doing so, she has made it abundantly clear her loyalties lie not with the United Kingdom, but a régime which is hostile towards the United Kingdom. She has therefore relinquished all rights and privileges that citizenship of this country permits, and her passport must be cancelled immediately, and let her be placed on an undesirable aliens list She can damn well apply for a passport from Islamic State or whatever they are calling themselves this week.
As for the children, she is their mother. If her actions have destroyed their liberties, tough! That's what happens when you mother is a terrorist-supporter.
The police claim not to have the manpower to investigate real crime like burglaries, (but they can always find the manpower to set up speed traps) so why are they wasting time investigating why some veil-wearing female has decided to become a baby-machine of her religion?