How would her return work, practically.
She's going to be a target for violence. A significant number of British racists would wish her harm. A rather larger number of British people (as on this thread) would not actually wish her active harm, but would be entirely indifferent to it happening. Her every move would be Twitter meltdown, and it's almost unimaginable that legal anonymity on the scale of Thompson and Venables would be granted to her.
Unless they have a political death wish, the British Muslim community would treat her like kryptonite alloyed with plutonium. The vast majority of mainstream Muslims have spent the last ten years distancing themselves from IS, so to welcome her back as "one of us" would leave it for racists to say "see, they're all as bad as each other".
So the likely outcome would be violence against random Muslim women of roughly the same age, accusations of fifth column status against any Muslim organisation which put its head above the parapet, a return to the "Muslims are all IS supporters" narrative, in exchange for...what?
If I were a Machiavellian securocrat, I'd be offer a reward to anyone in Syria who shot her, and if I sent any British support, it would be a deniable ex-SAS mercenary carrying a Kalashnikov. Assuming we aren't living in a Tom Clancey novel, this isn't going to happen, but the British government would be very happy for her to die in a way which their hands are nowhere near. Because there is no way that her return to the UK ends remotely well.