I think I figured out who Rey is
Hear me out, this may be an existing theory already but this just dawned on me. Remember when Sidious was telling Anakin about Darth Plagueis, and that he could influence the midichlorians to create life? What if Sidious found out how to do this on his own in order to replace Vader as an apprentice and that's how he created Rey? Similar to how Anakin was born. Then Luke found Rey after the fall of the empire and was so afraid of her power that he hid her away on Jakku. That's why Luke is afraid to train her. What do you guys think?