Hard case this.
She was 15, simply put, a child when she went. In our society you're not allowed to make most decisions on your own at that age, because you're not mature enough to make them in an informed way. I don't know anything about her childhood, but I imagine her parents aren't wealthy and sophisticated people from North London.
On the other hand, she joined a terrorist group with whom she still agrees apparently. This does not speak in her favour, at all. She's made her bed and was quite content with it. That is, until it collapsed and she got caught. A very logic first reaction is feck off and die in your terrorist bed you cnut.
However, we are not ISIS,we are enlightened and believe in rehabilitation (don't we?). By giving her a second chance we can show the world we are better than them. Because say what you want about western democracy, they're morally superior to ISIS.
I still slightly lean to the feck off and die in a Kurdish prison stance , but not completely.