It is the job of the Home Secretary to keep the UK population safe, and the risk of allowing a former active Islamic State group member back into the country would set a dangerous precedent. If individuals leave the UK to join a terrorist organization, they should not be expected to be allowed to return to the country that they betrayed and sought to undermine.
If Begum was white and of ethnically British origin, the question of her citizenship would never have been raised. Begum was exploited and horrifically abused for years, and by the age of 19 had found herself a widowed mother who had lost three children. The reality is that, whether we like it or not, she is UK-born and raised. Begum deserves to — like any member of British society — face the responsibilities of her crimes in the UK.