We still don't know Rey's lineage, the subject of many online theories, but the novelization reveals Kylo Ren has some idea of where she comes from.
As Ren tries to probe Rey's mind for an image of the map, he discovers something of interest and attempts to analyze it when he discovers that she is blocking him from her mind. As she manages to get inside his head, the stunned Ren realizes she is strong with the Force.
During the lightsaber battle in the woods, Rey uses the Force to draw Luke Skywalker's lightsaber to her hands, bypassing Ren. All that happens just like in the film.
But in the novel, this turn of events leads Ren to mutter, "It is you," showing that he already knows, or has a sense of, who she is.
"His words unsettled her: Not for the first time, he seemed to know more about her than she did about herself. But she had no time to ponder his comment, nor was she inclined to do so anyway; she was too consumed with rage," the novel explains.
During this scene, the novel also reveals Rey "recoiled" from the Dark Side as it pressured her to kill the wounded Kylo Ren.