shamima begum and amira abase , both 15 , and kadiza sultana , 16 , crossed over the turkish-syrian border last february and are believed to be living in the syrian city of raqqa .
begum has forged social media links with three of the british leaders of the al-khansa brigade .
it is understood the trio are now training with one of the notorious females arms of isis that savage beatings on the streets of raqqa and spying on its citizens .