Kayla Mueller was a 26 year old woman who went to the Middle East of her own free will. She was reported to be a "aid worker" although she seemed to mostly do office work. She got kidnapped while she was in Syria on a day trip.
The 14 year old is a Yazidi young lady who was captured when ISIS overran her village. She is the one who escaped and got to the Americans to tell her story.
This chick was an ISM member like Rachel Corrie. She got the slow motion bulldozer. Too bad, so sad.