I have been watching several clips that displayed the enormity of Darth Sidious’s power in both the Force and in lightsaber combat. Darth Sidious was easily one of the most powerful Sith Lords who ever lived and one of the most proficient masters of the Force the galaxy has ever known. His lightsaber skills were deadly enough to cut down three Jedi Council members in quick succession, versatile enough to defeat Darth Maul and Savage Opress, and powerful enough to fight Mace Windu as an equal. His mastery of the Force was complex enough to fight Yoda to a draw, mysterious enough to cheat death, and strong enough to demolish entire fleets.
What is even more fascinating is that all of this power and potential flows in Rey Skywalker’s veins. She has it in her to become a Jedi version of her grandfather. That would make her a real force to be reckoned with while fighting agents of the dark side. The only reason why she was able to defeat her grandfather is because her hereditary power was being augmented by the combined strength of all the Jedi who came before her. Even after defeating Palpatine, the exertion of fighting him briefly killed Rey. Due to this, she is nowhere near the height of her grandfather’s power and could not become his equal on her own. However, with enough time and training, she will become as powerful as her grandfather if not stronger. Who knows? Rey may become what Luke Skywalker became in Legends: the ultimate Jedi!
Due to her Sith heritage, Rey naturally has an affinity with Force Lightning. That power will always be a part of her, which means sooner or later she will need to learn how to control it. I think she could use Force Lightning in a similar fashion to how Mace Windu used his personal lightsaber style known as Vaapad. Vaapad allowed Mace Windu to convert his inner darkness into a weapon of the light. Using this method takes the wielder through the penumbra of the dark side. Due to its aggressive nature and tendency to lure its wielders dangerously close to the dark side, only a handful of Jedi were allowed to learn it. In the end, Mace Windu was the only Jedi who mastered Vaapad without turning to the dark side thanks to his strong willpower and extensive training. I think Rey will master Force Lightning in a way that is similar to how Mace Windu mastered Vaapad. In addition, Rey may forbid teaching Force Lightning to her students out fear that it could turn them to the dark side.
Overall, I am envisioning Rey Skywalker eventually becoming a female version of Starkiller from The Force Unleashed. Thanks to Rey Skywalker, the power of Darth Sidious, which has been an instrument of evil and a weapon of the Sith for decades, will finally be used for good and become a weapon of the Jedi.