I'm sure that after the war there were a great many Germans denying they'd ever supported Hitler or the Nazi Party - and that many of those denials were false. Conversely, I guess it's also true to say that if you were German born and bred and living in Germany in the 30s and through the war, it was very difficult, or unwise - to say the very least! - to turn round and say, No, that Hitler bloke's got it all wrong, killing jews is wicked, he's a raving psychopath and needs to be stopped. I suppose a few did - but they were unlikely to be around to tell their stories after the liberation in 1945!
There is a big difference between being caught up in an inescapable situaltion a la Winston Smith and playing along, and making a deliberate effort to travel hundred of miles in order to team up with murderous loonies. Yes, OK she was only 15, and almost by definition, a half wit, legally a victim on account of her age, but I alsolutely wouldn't exonerate her by arguing (as you must) that she was forced by circumstances to flee to Syria and then, horror 'pon horror, find to her surprise that ISIS are not a pressure group made up of muslim social workers, then have to fit in with them (including, by definition, submit to forced marriage followed by rape)....or else....I know Germans who have family members who were members of the nazi party and fought for Germany in the war. Their story is as far from Miss Begum's as mine is from that of Elvis.