This is a new phenomena. Young women, obviously believers in their faith, are being groomed by enablers into becoming brides for the monstrous fellows wreaking mayhem in the ME. Obviously these women and girls are drip fed piffle about sacrifice for god among other bilge and they make their way to these places to be sold to fighters.
How do we deal with this phenomena? Obviously the front line is the Muslim community. They must be prodigious in their output of counter jihadi messages and most specifically be concerned that these messages reach their children.
Then there is the community at large. While the governments can make sure that underage are not traveling without a parent or legal guardian, they must also block them at check points where they leave if the reasons they give are spurious.
If all of these are in place and they still go then we must take care of what will await them on return. They cannot come back to the community. They are at that point toxic. They must be tried and serve time if convicted and when that is over have restrictions to their movement and be placed in a national registry.