I strongly suspect that the girl’s lives have become so horrifying, multiple rapes per day, beatings, starvation and etc, that they see the suicide bombing as a way to end the pain.
They are probably easy to convince to do it.
If I were President... the response would appear to be the Wrath of An Angry God.
They don’t volunteer. They are left in the area with bombs strapped to their bodies which are detonated remotely by the terrorists. These are not suicide bombers. They are victims of murder.