I am in absolute agreement with those above.
Almost every year a case hits the headlines of children the age SB was when she went to Iraq, running off with teachers, people who have groomed them on the internet (as SB was), men they meet on holiday and so on and for everyone that hits the headlines another 100 or so, if not more, are intercepted or are missing only hours. Nobody thinks twice about retrieving these children and restoring them to their families. I can see no reason why SB should not be treated in the same way.
As for her citizenship, she was born and brought up in this country, she is a British citzen. Good heavens, a huge swathe of the British population, including me, could get a passport for another country through parents or grandparents. Are we all to live in fear that if we do anything that upsets the government, we will have our citizenship withdrawn and be sent back to Ireland, or belgium or Sweden, or the USA, to name the 'second' country in mine or my friend's family story?