I think this is a very dubious piece of dogwhistle politics which will stick so long as she is represented by a community lawyer for community people who would be more at home doing conveyancing, but will collapse like a house of cards if a good international human rights lawyer gets involved.
That said, I can't say I find "de-radicalising" terribly convincing. Her family are religious fanatics, and the track record of "de-radicalisation" is non-existent. Plenty of terrorists who have actually done terrorist shit have had prior engagement in such programmes, and there is no evidence, and precious little anecdote, which says they work. We can't intern her. We can't jail her long-term because she hasn't committed serious crimes for which we can provide UK-standard evidence in a UK court. Extra-judicial killings aren't quite cricket.
I presume the hope is that the Bangladeshi government will do nothing, and is in any event not capable of doing anything, so she will remain in Syria. Then either someone will kill her or the Iraqi, Turkish or maybe even Syrian authorities will try her and either execute her or imprison her for life.
It's cynical, dog whistle politics and it makes us look like Trump, but unfortunately it's hard to see what the plausible alternative is. She would be out free in the UK in a few years, the chances of her being "de-radicalised" are approximately zero and she would make a very serious rallying point for extremists. This is a bad, ugly, cynical outcome, better only than all the even more ugly alternatives.
This is what I think. But better written.