Leia ordered her to go to Ahch-To to find Luke Skywalker. Rey feels that the Force is guiding her and that her decision (to go) is the right one.
Rey headed to the launch area with R2-D2. Leia waited near the boarding ramp. She adjusted the fit of the new flight jacket Rey wore. “I’m proud of what you’re about to do.”
Rey looked into Leia’s eyes and saw more than pride. “But you’re also afraid. In sending me away, you’re…reminded.” Leia let go of the girl’s jacket. “You won’t share the fate of our son.”
Rey glanced at the Falcon. Chewbacca had almost completed his exterior flight check. “I know what we’re doing is right,” Rey said. “This is how it has to be. This is how it should be.”
“I know it, too,” Leia said. “May the Force be with you.” She moved back and smiled as Rey boarded.
Star Wars: The Force Awakens - Junior Novelisation
She felt more alive than she ever had on Jakku. She had a destiny. It
was big and frightening, but she had friends by her side to help her.
Her life was only just beginning.
Her life would never be the same. She might never return to Jakku. She might never reunite with her parents. Finding BB-8, meeting Finn, running into Han and Chewie—a series of accidents had led her there. This time, she wanted to make the choice.
“If it were you in my place, would you go?” Rey asked.
Leia sat next to Rey and took her hand. “That’s a decision only you can make.” Leia paused for a moment, then continued. “But when you do decide to go—”
Rey began to protest, but Leia raised her hand. “Trust me, you will. And when you do go, promise me you’ll be careful.” She shook her head. “The Force is powerful. I know you must have sensed it when you fought Kylo. The temptation, the darkness can be…”
Rey didn’t need her to finish. She knew that Kylo was Leia’s son. The idea that the child of two such extraordinary people could fall to the dark side was frightening.
But Rey would not let fear of the past stop her from embracing the future. Leia was right: Rey had a journey to go on.
The Force Awakens: Rey's Story