She is Anakin Skywalker.Why else would she have powers greater than Luke and Ren and everyone else?
Luke doesn’t have anywhere close to the intense reaction in A New Hope that Rey does in The Force Awakens when seeing Anakin’s Jedi lightsaber for the first time.
He even picks it up and waves it around with no reaction whatsoever. Not so for Rey.
In her vision there is darkness and light, pain, anger, hatred, the sense of abandonment Anakin felt as a boy and later as a man when Obi-wan struck him down, thus pushing him fully into his hatred.
The Star Wars Rey character, in that scene, is awakening to the fact she possesses all the same powers Anakin did, and she is terrified by it because she knows the history surrounding that weapon.