I’m torn really. On the one hand, she was old and evidently intelligent enough to understand that she was going to join brutal terrorists who thought nothing of killing/blowing up people who had done them no harm.
On the other, given her probable upbringing, very likely she was tightly controlled/restricted, compared to many other girls of that age.
I can’t help thinking that those girls my well have had some rose-tinted, romantic Mills and Boon-y dream of running away to marry a handsome warrior - a huge adventure which would undoubtedly shock and appal their families - but it was all in the name of Allah, so that made it all right.