15 years after the end of the Star Wars sequel trilogy, Rey has the potential to be more powerful than ever in the New Jedi Order movie, but Star Wars: The Rise of Skywalker made this very complicated. The final film of the Skywalker saga showed how powerful Rey had become, but the ending left her power levels uncertain. Following the Resistance celebrating their victory at Exegol, the movie had one scene with Rey on Tatooine, using the Force to bury the Skywalker lightsabers and see Luke Skywalker and Leia Organa through the Force. Her remaining power beyond that is largely unknown.
This means there are two main possibilities for Rey's story in the New Jedi Order movie. The first is that she is just as powerful as she was in the sequel trilogy, perhaps even more powerful than she was 15 years prior. Another possible outcome is that she is no longer as powerful as she used to be, which would lead to a very different story compared to the sequel trilogy. The complicated nature of The Rise of Skywalker also means the New Jedi Order movie could do something unexpected, but the film contains evidence for both of the main possibilities and hints at how powerful Rey will be going forward.
Rey's Power Is Tied To Her Being Part Of A Force Dyad 
The Rise of Skywalker revealed that Rey and Kylo Ren were a dyad in the Force, meaning a great deal of her power came from this bond. Palpatine described the Force dyad as "a power like life itself," so it would be appropriate to compare it to a wellspring that Rey drew on. According to Star Wars: The Last Jedi – Expanded Edition by Jason Fry, Rey even absorbed a degree of Ren's knowledge and training when he tried to enter her mind in Star Wars: The Force Awakens. The Force dyad gave Rey a lot of power, but this also creates a potential problem for The New Jedi Order movie.
