//She gained full criminal responsibility for herself when she became 14 years old…//
Just on a point of order, the age of criminal responsibility in England and Wales is ten.
//spice: "Can they still appeal to that European court? " - nope, that's one of the reasons we left the EUSSR.//
As pointed out, Tora, the UK is still a signatory to the European Convention on Human Rights. As such the European Court of Human Rights can be asked to rule on this matter. Whether they Ms Begum will take an appeal there is unknown. Although our own Human Rights Act (on which the Supreme Court would certainly have relied on in their deliberations) near enough mirrors the ECHR, if it was heard in Strasbourg there would be no guarantee the verdict would go the same way.